New iMac freezes?

Question

I received my new 24" 2.8GHz iMac in early November w/4GB of Crucial memory, immediately repartitioned it, upgraded to Leopard, migrated my apps/accounts/data over from my 2.7GHz G5 Tower (which has been running Leopard perfectly), and ran Software Update to bring everything current.
This Mac has not experienced any obvious video artifacts, or freezes while processing intensive video activity, but it is heavily customized. Here's the details:
I've attached an Apple 23" Cinema HD Display for dual displays, a G-Tech 750GB FW800 drive for Time Machine, and a Kensington USB 2.0 powered hub to attach all my USB stuff (Harmon/Kardon SoundSticks, SanDisk memory card reader, extra Mighty Mouse, USB dock for iPhone, Canon LiDE 30 scanner, USB connection to APC Back-UPS RS 1500). I retired my old USB 1.1 hub, since I knew it would be problematic with the new system, as would be my old USB Serial Adapter.
From a software viewpoint, I have iWork '08, iLife '08, Adobe CS3 Suite, MS Office 2004 11.3.9, Indigo 2 (home automation control software), Meteorologist, and all the other usual Apple software. At login, I have Mail, Indigo 2, iTunes, iPhoto, iCal, Address Book, Meteorologist, and Activity Monitor startup, then share iTunes and iPhoto over the local network. I also share my data volume over the local network, as this new iMac is replacing our old Windows 2003 server as a home media/data repository.
To add to the mix, I'm also running SereneSaver Quicktime movies as Desktop backgrounds cycling every 5 minutes on both displays (although it only displays the first frame of the video on the secondary display). I was also running MacKiev's 3D Atlas Globe screen saver (displaying the latest satellite cloud cover) until I found it was locking up the new iMac in about 3 hours (with SereneSaver also running). Needless to say, this all ran perfectly on the old G5 Tower, even with its ancient ATI Radeon 9800 Pro (128MB) video card. And finally, in addition to the regular .Mac/iDisk updates, and the hourly Time Machine backups, and the quarter hour Meteorologist weather updates, and the every 5 minutes Mail updates, I was using Spaces to sort out all the windows that I wasn't hiding.
I knew I probably brought over some conflicting software, since this was a migration from a PPC Mac to an Intel iMac, so when things froze, I assumed it was a compatibility issue, and proceeded to start trashing obviously unnecessary stuff from the system/root/user libraries. I also assured everything that was running was current. Over a couple of days I thought I had pretty much found everything I could think of that might crash the new iMac (including old Symantec frameworks, MS Virtual PPC stuff, old auto startup Retrospect stuff, and the like). I tested all my apps, reran the Leopard 10.5.1 combo update, Repaired Permissions, Verified Disk (with Disk Utility), booted up from a Tiger 10.4.11 volume and checked the Leopard startup with DiskWarrior 4.0, and then ran Apple's Hardware Test from their iMac startup DVD. In the end, I was able to keep the new iMac up and running continuously performing its assigned chores for over 37 hours.
Then, yesterday afternoon in mid-post to one of these threads, my shiny new iMac froze up. No warnings of any kind. In mid-breath it simply stopped working. The blinking colon in the menu clock stopped, the Activity Monitor CPU history graph updating in the Dock stopping updating, neither mouse would move, pressing any combination of keys on the keyboard I could think of would not interrupt the iMac from its pause. So, I sucked it up and pressed the power button to restart.
Upon restart, I checked the Console logs, and of course, nothing untowards was identified there. Whatever froze up the iMac happened immediately. A close Apple contact of mine immediately suggested it sounded like a hardware issue. I didn't think so, but I took his advice anyway and reinstalled Leopard in a virgin partition on the internal hard drive, along with iWork '08, iLife '08, and all the latest Apple updates, again. I did not install Adobe CS3, since its installer disk doesn't finish properly in Leopard, and I didn't want to install Tiger first, then all it's updates, then CS3, then all its updates, then Leopard again. I just want to confirm, or not, that I'm having an obscure hardware issue.
Today I'm running the virgin installation (now 16 hours into the test) to see if I can crack the 37 hour barrier. If I make it to two full days, I'll be pretty confident that I must still be having software issues with my standard startup configuration. Of course, I'm not currently running any non-Apple software, and there's no legacy stuff on this startup partition, other than the music and photos I copied over from my data partition for sharing over the network at home. I'm also foregoing Indigo 2 controlling stuff around the house, and the great SereneSaver Quicktime movies playing soothing videos (beach scenes, peaceful lakes, mountain vistas, etc. with background sounds) as my Desktop background.
So, if this basic, virgin configuration locks up in the next day or so, my next step is to pull the Crucial 4GB of memory and put the standard Apple 2GB back in, and wait another couple of days. If that locks up, then it's a call to AppleCare. If not, then it's a call to Crucial to replace their memory modules.
My question is whether anyone else with a simpler configuration, and no obvious video issues (as confirmed by Software Update not offering the video firmware update), is experiencing any spontaneous freezes?
At this point, it's still premature to think I have a hardware issue, but if I do it should manifest itself with this basic, virgin installation.
More updates later...

Answer 1

I have been experiencing a Restart/Shut Down reliability issue with my new iMac and Leopard 10.5.1. This evening an Apple rep I know pointed me to a work-around in Apple Discussions:
http://discussions.apple.com/thread.jspa?messageID=5957261&#5957261
This thread notes the discovery by one user that iDisk automatic syncing is not working reliably, and is preventing consistent restarting/shutting down of your Mac. Although, syncing has been working reliably for me both for .Mac stuff, and the iDisk itself, if you do a Get Info on your iDisk it reports, at least for me, that its capacity is 1TB, with 466GB available. I have only the standard 10GB .Mac account, and only 5GB of that is allocated to my iDisk, so something is clearly amiss with the .Mac iDisk setup (iDisk Get Info reports correctly on my G5 Macs w/Leopard), as being reported from the .Mac server. If you check your Console logs, you may also see this recurring error message, which is reporting a syncing error, although my syncs have, as I've said, been working correctly:
11/25/07 9:11 PM FileSyncAgent192 MKCOL /.FileSync (FAILED), httpStatusCode:405, errorType:100, transactionState:5, txnId:3846B904-9ABB-40E5-9928-B9233FAC05D2, auto-retries=0, manual-retries=0
To summarize, if you turn off your iDisk in your System Preferences/.Mac/iDisk preference pane, you'll have no problems restarting/shutting down. You may also need to do the power management reset (turn off Mac, unplug all devices and power for 15 seconds, reconnect, and start up) and the parameter RAM reset (reboot while holding down the cmd-opt-P-R keys). You can do this in one restart cycle, if you like. After that, restarts/shutting down has worked perfectly for me.
Of course, I actually USE my iDisk, and will be leaving it on. But, at least I know now how to work around the restart/shut down issue. (Note: this morning my iMac running my full/standard configuration locked up, after the iDisk mounted/unmounted repeatedly during the evening, so I rebooted and switched iDisk syncing to manual. More to follow...)
I hope Apple adds this fix to their 10.5.2 update next month.
Note: This is such an important issue, that in addition to adding it to a reply in another Shut Down thread, I thought I'd post it as a separate topic here.