Lose focus within a active window within 2 to 4 seconds.

I have never installed Hyperspace - unless it came with Lion? I'm assuming you are refering to this program: http://thecocoabots.com/hyperspaces ?

Maybe we are having the same symptoms but different root causes?

I'm having the same issue on 2 different MacBook Airs - the 2010 & 2011 models. The 2010 model worked fine until I upgraded to Lion - so I'm sure that's part of the problem.

Both have more or less the same software - just the basics like Office 2011, Dropbox, etc. No system tweaks or even utilities.

Apps start to lose focus after about 15 to 30 minutes of use, starting with email clients - but eventually affecting almost everything.

I've stopped almost ever running process, re-installed Lion...

So now I'm at the Firewall - the only thing I can think of that both machines had in common (I turned it on for both). So, with the Firewall off, so far (a few hours) so good - but I've said that before.

Will post the outcome when it happens. Thanks!

Finally isolated my particular problem: It's Adobe Air + Chatter Desktop for SalesForce. After deleting both I haven't had any problems for 2 days.

For me Adiobe Air and Chatter seem to have been the problem. However, I appear to have solved the problem simply by closing Chatter Desktop. Mail window now retains focus.

I had the same issue. Type one letter in To field, and window loses focus. All I did was quit the Chatter Desktop application and the problem went away immediately. Did not have to reboot, uninstall Adobe Air, or even restart Outlook. Simply quitting Chatter Desktop did the trick.

Quick update. If you have chatter desktop running, it appears you do not even need to quit that app. Goto settings and uncheck "enable notifications". I restarted chatter desktop this morning with that box unchecked and have had no problems all day.

For anyone having this issue, try uninstalling Microsoft Office 2011 before reinstalling Mountain Lion from scratch. It worked for me.