Various process crashes prevent login to main user account

Question

Here's a good one. I can't log in to my main user account; here's the recap:
Computer was acting slow and pausing a lot over past couple of weeks; I put it down to internet slowness at first, but after awhile I began closing down less-critical processes like .mac synchronization, mySQL, etc. Can't recall running any new installs recently, or updates, except perhaps Firefox.
Checked the logs, saw that my old pal mdimport was crashing repeatedly, like every 15 seconds or so. That will slow things down! So I turned off the Spotlight indexing for all categories, and eventually made the hard disk a private item. mdimport still crashing.
Ran permissions repair; some problems fixed, nothing too alarming in the logs (I think). Verified the hard disk; no problems found.
At some point the main account became unable to log me in. The login window accepts a password and disappears, but after a little while a blue screen appears, and the login window returns. I am able to log in using a secondary more-or-less virgin account on this machine, which seems to work fine.
Console logs reveal the constantly crashing mdimport, triggered anytime I attempt to log in using the main account. Secondarily, the loginwindow process is crashing on login (main account only) and crashdump itself is consistently crashing just afterwards. Occasionally another process called lsregister will crash at the login attempt, sometimes other processes too. More worryingly, there are reported IO errors from the kernel.
I've reset the pram, I've reset the nvram. I've booted from a 10.5 system disk and re-run disk utility for permissions and repair disk. I tried safe mode.
I've attempted to rsync my main user account to another computer while booted to target disk mode; rsync (running on the remote machine to which I'm copying the files) copies the many gigabytes in my Documents folder, but chokes consistently at some files in my Library ("former iDisk.dmg", App Support/firefox/profiles/etc, also some Growl files) with "Input/output error (5)."
Anyone have any good theories? Many thanks in advance.
--David H

Answer 1

Thanks for your reply; I checked out the links but nothing seems too directly related. I'm vaguely aware of what mdimport does, but I certainly have seen it crash a lot.
At this point, I'm finally able to log back in to my main account, which (with some caveats/questions below) seems to be working.
To get back to this point, I used the terminal utility Applejack to clear caches, check plists for corruption, and clear virtual memory. I also manually deleted a loginwindow plist and some Library/Caches/com.apple.LaunchServices/ files. Something in there seemed to help, and I'm finally back in to the main user account. There was definitely no getting into this account before I tried these steps.
Applejack is found at http://applejack.sourceforge.net/.
I still have some troubling log entries, and some blips in several files. While subsequently backing up my user account, rsync consistently tripped on several files in /Library/Application Support relating to Firefox and Growl, in /Library/iCal, and also a couple of image files (out of tens of thousands) in my Pictures folder. So I deleted these files; the only concern so far is the iCal file which was called "corestorage.ics." And now that I've started iCal, it looks like I still have data; but my console log shows about 70 lines of "Calendaring data empty." Ugh. Nothing like losing data but not knowing what was lost.
Also troubling in the system log: I have several entries of "kernel[0]: disk0s3: I/O error" (though not in the latest reboot cycle). Hard to tell if these belong in the same category as the many cryptic and possibly alarming messages seen there, or if this is a real warning of a failing hard disk, or of other corrupt files the system is running into. Again, disk utility has repeatedly found no problems.
(Also I have several hundred entries of "/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metada ta.framework/Versions/A/Support/mdimportserver: _TIFFVSetField: tiff data provider: Invalid tag "Copyright" (not supported by codec)", which I hope relate to mdimport seeing many jpg images that have copyright metadata. I'm hoping that problem will go away now that they're marked "private" as far as Spotlight is concerned.)
At least I'm back in the account. I'm trying to decide whether to archive & install system 10.5; I'd prefer to reformat a misbehaving disk, but then you gotta have pretty serious confidence in your backups. Alternatively if the rumors are true I'm hanging on for one of the new laptops; I'd prefer that to replacing the hard drive again in this diabolical case. (Price you pay for sleek, I guess.)
Time will tell.