10.5.2 - Mail hangs; generally sluggish; messages don't display

Question

Since upgrading to 10.5.2, I'm experiencing various issues with Mail.app:
• It takes a long time to launch, and often hangs without ever fully launching, requiring a force-quit and relaunch.
• After launching, there's a general sluggishness throughout the app. The initial "checking for mail" sequence takes forever -- sometimes never completing.
• Often, items I select take far longer than normal to display; messages I select aren't displayed at all; or mailboxes I select -- mailboxes that say they contain messages -- will display no messages. (This behavior is sometimes accompanied by the spinning beach ball, but not always.)
• I sometimes have to force-quit and relaunch 3 or 4 times before I can actually use the app.
Users on other forums have reported similar issues. Has anyone discovered a fix for these issues?
Otherwise, Apple, we really need assistance, here. Needless to say, this is severely disruptive to our workflow and everyday lives.

Answer 1

My issue turned out to be for more complex than I realized. In addition to Mail.app's sluggishness, all of my syncing (calendars, contacts, mail, bookmarks, iPhone) had also ground to a halt. In System Preferences>.Mac, I was unable to even select the "Sync" tab. (Doing so "crashed" the System Prefs window and made the processor run hot, which made the fan come on.) So, with Activity Monitor, I traced the problem to the Sync Server.
A search, here in the discussions, led me to several users who had identical symptoms after installing Leopard or a Leopard update -- but no solutions. Finally I went to another Apple-related forum and found a solution. Someone there wrote:
+"trashing the ~/Library/Application Support/SyncServices/Local/ folder did it... Usually touching that folder brings good karma..."+
It seemed like a radical move, because on my MacBook Pro that folder contained over 500 megs of data (although I now suspect it was abnormally bloated). But I had everything backed up, so here's what I did:
1. I moved the folder, referenced above, to my desktop. (Note that "~" indicates your home folder.)
2. Restarted my macine.
3. Opened the .Mac preference pane, then clicked "Sync"
(Note: Previously, clicking "Sync" had been causing the Prefs window, so just being able to bring up that window was a huge victory.)
4. Clicked the "Advanced" button, selected the MacBook Pro, then clicked "Reset Sync Data" and made sure that I was replacing data on .Mac with the data from the computer (which I knew was good data). In other words, I made sure that the animated arrow was moving away from the computer and toward .Mac, indicating the direction of the data transfer.
(The folder I deleted in step 1 contained a lot of sync data. So without step #4, I was concerned that .Mac -- with its data having been deleted -- might have interpreted that as a signal to delete the data on the Mac. So I performed step #4 to make sure that didn't happen.)
5. Then I clicked "Sync now."
This was the first time I'd gotten sync to work for at least 36 hours. Also, after the sync was completed, the new "Local" folder, which replaced the one I deleted, only had 62 megs of data. Hence, my suspicion that the deleted folder was abnormally bloated.
So far so good.... I've got sync, and Mail is launching much more quickly now. Fingers crossed, but everything seems to be working well.