Be careful with over-doing it. Too much can make your sprites look noisy and blobby, in my opinion. Like you just down-res'd higher resolution sprites using dirty tools. Your blur haired guy is looking pretty good, but the necrodruid is starting to look a little noisy, I think. The generic "subpixel animation is awesome!" tutorial shows the dangers of sub-pixeling best, ironically:

Sure, that small sprite is holding a lot of information, but is it really a good look?
I've seen some nice examples of sub-pixel animation, though. But I can't find any of them right now! And the only one I can think of off the top of my head is one of the member's avatars here. The guy with the orange slime/poring-like creature. I haven't seen him around in awhile, though...