For those of you who may be running the M3 build of Windows 7 and using either hosted Exchange or accessing a corporate Exchange environment via Outlook Anywhere (nee RPC over HTTPS) there is an issue you may run into.
When you try to open Outlook you are prompted for credentials. With most hosted Exchange providers you use your email address as the username. If you do this on Windows 7 (M3) I have found that you are repeatedly prompted for your credentials but no matter how carefully and correctly you type your password it just keeps prompting you.
If you run into this issue try entering you username in the DOMAIN\Username format instead of your email address. I don't know why this works, but I know it does for at least two Hosted Exchange providers. Contact your hosted provider if you are not sure what the domain name is.