Beta 3 sometimes seems to be very slow for me when moving the cursor using the up/down/left/right cursor keys (bound to the normal cursor-up/down/left/right commands). It was practically unusable a few minutes ago after opening a project. Just pressing and holding one of the cursor keys would move the cursor 3-5 lines or chars, pause for a second, move a few more, pause, etc.
I just switched back after starting this post, and now it seems OK. Was VS doing some background processing? Process Explorer was only showing minimal CPU usage though (1-3% overall at the time).
I'm running the Windows x64 version on Windows 7. System is a Core i7-2600.