It's a very cheap trick and most likely nothing new, but since I'd never seen that anywere mentioned before I just post it here.
Basically it's just abusing the texture filtering... just leave a small (*) transparent border et voila - the edges start to bleed around.
(* 1 pixel width shown on the screenshot - tryed also 2px but it didn't make a difference)
I would say the quality is about as good as 4x rotated grid antialiasing, wich is pretty good. It's isn't 100% free since you need a third more vram for the textures (if they were without alpha before) and you'll need a bit fiddling around, but there are some occasions were you can use this stuff.