What sense would 65 x 65 make? 60 x 60 is AIM's size. 100 x 100 is MSN's size. Those are the only reasonable sizes to be used. I think 60 x 60 is perfectly reasonable. However, I'm not too fond of the 6 kb limit that limit seems to come out of no where. I doubt that'll ever be changed though.

I like MecaKane's idea. I could so easily resize my sig to 60 x 60. =D