I've been using this beta build on my work laptop, home desktop, and netbook for about a month. Very stable, haven't had a single issue. Also, lots of very nice Outlook enhancements if you're using an Exchange 2010 mailbox server.

Be aware that a lot of 3rd party plugins, specifically Outlook plugins, won't work on the 64 bit version of Office. I recommend installing the 32 bit version.