If Twitter likens its service to the twittering tweets of a bird, then Jaiku likens its own to, well, haiku. Not that Jaiku is an exact replica of Twitter, though. You can not only micro/nano-blog, you can also add other online presences of yours: blog feeds, Flickr photos, del.icio.us bookmarks, or anything else that carries a feed. (Twitter included!)
Why do Web 2.0 sites have a fondness for Japanese-sounding words?