Can't believe all the people having issues with Lion in this thread. Besides the CUI CUI CUI error, which is an actual problem. (Or just complaining about feature requests, most of the time).
There is a way to troubleshoot your issues, you know.
1. Do a clean install.
2. Don't restore anything from a Time Machine Backup. Manually copy and paste your documents to your new install.
3. Install your applications one by one, restarting your computer and going awhile without installing another one to note any performance changes.
4. Identify the problem app.
This sort of stuff is what you always hear from people offering tech support for troubleshooting Windows PCs.
It is a waste of time in 90% of cases, but it keeps people busy and out of their hair for a day or two.
Whatever happened to "it just works"?