I am finding that both IE8 and Chrome are locking up and it seems to be related to the SP plugin. I also find that in Chrome,SP is failing to populate fields (including logging in to this forum).
In Chrome, when the program becomes unresponsive if I right-click the SP Icon and 'Disable', it instantly starts working normally.
I am testing on Windows 7 x64 and x32. (Using 32-bit IE8 on both).