Is making the option to turn off avatars a simple operation?
It's designed to be a marketing ploy. I already offer 50k one's. Nobody seems to make use of it though. I imagine you would have to specificly make even a 1mb av at 150 x150 pixels. They would be cool though. Maybe a good gimmick.
You have to remember that for anyone on an 800x600 resolution, the avatar will take up 1/5 of their screen. Most forums stick to the 60kb 60x60 rule, which won't slow down the site much, and keep it reasonable.