I recently noticed some ugly aliasing in the sidebar site list:
I actually solved this problem before in my SE app (no linky here, that would be bad. It's in my profile). It turns out you can't just put a big UIImage into a small UIImageView. You have to resize the image itself.
What I did was use
UIImage+ProportionalFill from the MGImageUtilities. I replaced:
UIImage *img = [UIImage imageWithData:imgData];
UIImage *img = [[UIImage imageWithData:imgData] imageScaledToFitSize:CGSizeMake(30, 30)/*<-- Put your size here*/];
And that makes it look a whole lot better.