So there's this new image upscaling utility at http://waifu2x.udp.jp that apparently involves machine-learning and optimization specifically for anime-style artwork.
Posting this here FYI because it's a pretty good tool, but more importantly because a few upscaled images seem to have been uploaded here already and more will surely follow as this thing gets more popular, so approvers should be extra careful when considering for approval larger versions of existing posts.