It's been about a year since the release of Visio 2007 and Office 2007, and Microsoft has now published Service Pack 1. Here is the download link for English. You can choose another language from this link as well.
The goals of this service pack are to provide compatibility for upcoming releases such as Windows 2008 Server, improve security and address key performance and reliability issues.
A specific fix to note for Visio:
The KB article with all the details is here: