I have had the same issue, intermeddiately.
I have Avast and Live Maps (
http://outlook.maps.live.com/minisites/local/outlook/default.aspx) plugin/addin, no other non-Outlook plugins/addins in Outlook 2007, and I'm running Vista Home Premium SP1.
I have the latest release of Avast, 4.8-1169
2 Things I noticed:
1. After ending the Outlook process with taskmanager, (BTW - there are 2 outlook process running when this happens), and restarting Outlook I get the Avast plugin warning, but I also get a waring for the Live Maps plugin for MS Outlook.
If I disable Avast plugin, but leave Live Maps running, Outlook does start normally. This "leads" me to believe that Avast plugin may have a compatibility issue with other Outlook plugins that access a network or the internet.
2. While Outlook was "hanging" I terminated the the INTERNET MAIL module in On-Access and BAM Outlook immedaitely stopped hanging and started. I then restarted Internet mail and there where no issues, YET!
The problem seems random and I can't reproduce it at will, when it happens again I will disable Internet Mail and see if I get the same result. If I don't then I will deactivate Live Maps and see what happens.
Clearly the Avast plugin works in isolation, but it seems to be incompatible with something else in Outlook or MS Exchange.
FYI: Live Maps addin, allows Live Maps to be used and saved in Outlook calendar appointments, it does access the Internet as if you where using a browser.