Personally I always like to know how the others I am working with look like. This makes is also easier in case one actually meets one other.
Gravatar is actually pretty easy to use, you only need to calculate the MD5-hash from an emailaddress and append that to a URL:
$ echo -n firstname.lastname@example.org | md5sum 9f9a7a129db9c1065c011dba45c3cee9The emailaddress is a fake one, the md5sum is real though.
Now the URL http://www.gravatar.com/avatar/9f9a7a129db9c1065c011dba45c3cee9 (optionally append .gif, .jpg, ...) can be used to retrieve the avatar:
Of course this only makes sense if you have an icon of yourself. I created my current one, using The GIMP with some help from the following sites: