Before upgrading to Lion I had no problems with Xcode or other application freezing and becoming "not responding". After upgrading, Xcode, which I use all day in my work, often freezes, sometimes other applications too. Usually it returns to normal state if I wait 1-5 minutes, but sometimes not and unsaved data is lost when I have to force quit Xcode (before I discovered how to quit Kaspersky's process). The really bad thing is that it's when saving that Kaspersky locks up the saving application so the chances of loosing valuable work is high.
If you are required to run Kaspersky on your Mac, I recommend that you do not upgrade to Lion until Kaspersky has fixed to support Lion's Autosave and Versions.
If Xcode or any other application locks up, open "Activity Monitor" and quit the process "kav". This will release the lock on the frozen application but (it looks like) Kaspersky will automatically restart so you have to repeat this every time an application freezes when saving data.
I'm not alone:
Cocoabuilder.com: Xcode4 and Lion causes freezes when saving
Stackoverflow.com: Xcode is very slow to save a file frequently beach balls
Waiting for a fix...