I just spruced mine up a bit and increased it to 200x200. Looks nice and sharp on my profile, but is rather blurry on my forum posts. Seems like some resampling could be done better.

From left to right: scaled image used in forum posts, image used for avatar, imaged scaled with Fant to 150x150
The latter two look much sharper than the first one
Edit: messing around with Chromium's zoom levels actually suggests it's a clientside issue. It looks sharp for 0.5s, then it loses its sharpness when I assume the browser does the resampling. Perhaps it would be better to just generate the required images serverside, and serve those as appropriate?