I've done some testing, I believe it's a Google Chrome issue.
Test 1 - Chrome
Changed Gravatar
Cleared all browsing data
Restarted browser
Still see old gravatar
Test 2 - Firefox
Changed Gravatar
Waited a few minutes
Could see new Gravatar
I think I may have found the problem. This could be completely wrong, but I've found that my gravatar doesn't update when I change the file type. The usual perma-link you get for your gravatar gets changed to the new file extension, thus, changing the url. Say you had...
So one second I was working on one of my groups username CSS and I go back to my site to have a look and the forums and categories and what not have disappeared. ( http://worldofguildcraft.net/forum/index.php ). My node tree in my Admin CP is still intact. File Health check came out 100%