WordPress 2.6 was released today and features lots of great new features (see following video). Unlike WordPress 2.0.x (2.0.11 currently) but like the 2.1.x, 2.2.x, and 2.3.x branches, the 2.5.x branch is now unsupported and will not be updated with new security patches. You should not put off updating. There is nothing to be scared of and it is unlikely any of your plugins or your theme will break. So do yourself a favor and upgrade!
One of those features is the default Gravatar picker I helped write. If you are a theme developer and wish to add your own default Gravatar to the list, check out my previous post.