I just have an epiphany.
Firstly, I'm running CM7 nightly from 6/22
@optikalblitz: You said Google Music was causing issues. I disabled Music sync, then went into the Music app itself to turn off any sync settings in it. When I opened the app, it loaded for a few seconds, then crashed. I had LogCat running in Eclipse, and the error was a File creation exception stating that I was out of space.
The strange thing is, I'm NOT out of space. My SD card and internal memory have plenty of room. Then I remembered: The Incredible only has about 300 MB of application storage partitioned. Cyanogen seems to work around this problem, EXCEPT for apps from the Marketplace. They will still say there is not enough space. Other install sources (raw apk, amazon, etc), work just fine.
I remembered that I installed Peggle from Amazon yesterday, which was an 80 MB download. I also remembered I couldn't re-install Angry Birds that day because the Market said I was out of space.
So! I uninstalled Peggle and a couple more large apps I don't need, turned all my syncing back on, no DB I/O errors in LogCat, no force closes, no nothing!
So here's my diagnosis:
-HTC Incredible only partitions ~300 MB for applications+data
-Cyanogen lets users install MORE than 300 MB of applications+data
-Android services (such as market and sync) don't understand Cyanogen is doing
-Android services fail gracefully (like market), or not so gracefully (like Sync) when you are out of 'storage'.
-Making sure you have some "free" space in your /data/data/ folder (I have about 30 MB) causes these force closes to stop.
Now, this only worked for me. I can't guarantee it'll work for you, but I was being killed by Force Closes all yesterday, and now they're 100% gone.
PLEASE post back if this works for you!