While were talking about Outlook not connecting – KB924625 mentions a number of issues you may face troubleshooting Outlook connecting to 2007/2010
While were talking Outlook and Exchange two articles are also super interesting:
Common Client Access Considerations for Outlook 2003 and exchange 2010 http://msexchangeteam.com/archive/2010/04/23/454711.aspx
Understanding rpc Client Access
And while were talking about clients and what they're doing:
Exchange Server User Monitor
While there's plenty more material out there, I wanted to put a marker in the ground and start somewhere – I'm hoping I'll update this post as I dig up more.