I installed Lion on launch day, and a few days after, my Finder sounds stopped playing. When I move files, or folders, delete items or empty the trash there is never any accompanying sound. I know this worked under Lion for a while, so I do not thing that the cause is the lion upgrade.
After further investigation, I discovered that the issue was not confined to Finder sounds but other sounds as well.
I deleted the com.apple.SystemSounds preference file from
~/Library/Preferences, restarted my computer and it solved the issue.