If you use EPM2007 and are thinking about upgrading to IE8, you will experience a visual issue in PWA > Home Page. The 'Reminders' and 'Project Workspace' webparts do not expand to the full extent of the window.
Note: Microsoft is aware of this issue. I am sure this will be resolved in the next cumulative update (CU).
click to enlarge
There are no known functionality/data related issues.