Ever since I upgraded to Lion, I've found that on occasion the Finder becomes unresponsive. When the Finder freezes, the entire system becomes unstable (anything that accesses the filesystem). Luckily, I came across a possible workaround and solution to this problem.
Before I found a solution, I was using a quick fix to get things working: manually relaunching the Finder.
This, however, becomes very tiresome. iTunes, Logic, the Adobe Suite, and other applications all freeze, rendering my computer almost useless. After searching through Apple support forums, one user suggested booting into "safe mode," opening the Finder, poking around, and restarting. It's very simple to do:
Once you've done this, use your computer normally. Hopefully it resolves your Finder issue; I've used it for a few days, and I have not noticed a Finder freeze since.
FYI: from what I've seen, this bug seems to be caused by upgrading OS X 10.6 to 10.7 via the Mac App Store. Apparently, a preference or other system file becomes corrupted, causing this issue. Doing the "safe boot" cleans up the corrupted file, and gets everything back to normal.
This may not work for you, and if that's your case, there are a few other alternative methods suggested in the Apple support thread: Finder Crash on Lion: Apple Support Communities.
One user reported that corrupted .DS_Store files caused his issues. To remove them, run this from a terminal window:
$ rm ~/.DS\_Store; rm ~/Desktop/.DS\_Store
This is probably the most difficult method, due to the sheer amount of time that it takes. For a complete set of instructions, I would check out this post.