The dimensions should be 80x80 and the size is 6144 bytes. The best avatars to have are jpg format because they are compressed. If you want to get technical...
Here is the reasoning:
A full 80x80 gif with 256 colors (which is 8 bits) is at most 6400 bytes.
A jpg can go 24 bit which means millions of colors. AND since jpg is compressed, you can get same image below 3000 bytes. This will reduce download times for those with less than fast connections (modems).
I want to keep this place bandwidth friendly
/Snafu