Did your GMail Notifier stop working a little while ago? Does it all of a sudden always sit there with an exclamation point instead of the envelope? Does it just say
An error has occurred.
Cannot connect to mailbox.
Service unavailable
every time you try to check your mail?
You probably just did the same thing I did when the latest interface came you, went through the settings and immediately checked the “Always use https” option. This turned out to the the problem. Notifier probably can’t follow the redirect. To fix it, you can uncheck the option, or, better yet, use a registry hack (from Google) to allow Notifier to also use SSL.
I certainly can’t take any credit for this, lots of other people figured this out before me, but those blog entries didn’t really come up high when I searched for a solution, so maybe this one has the right keywords to help someone 
.