The lack for single sign-on (SSO) certainly is one of the most critical entries into the Office 2.0 bug tracker. A fix is currently being developed by a Vancouver-based company called Sxip Identity Corporation, which authored the eponymous Simple eXtensible Identity Protocol (SXIP). It currently works with Salesforce.com, and I would expect more online services to be supported down the road. I will consider the bug fixed once SXIP supports Google as well.