There are a few people I know are using Skritter in my Chinese class, and so I found myself wondering about Skritter Friends. It may seem kind of pointless, but I was thinking about "competing" against each other (whether in total practice time, retention rate, number of characters learned, etc) as an incentive to practice. Between friends this could be simple comparison, but in the context of a class, this could be a measure of completion of the vocab list everyone is working on (which lends itself well to teacher/student accounts, ostensibly a part of volume licensing).
In the list of "things that are unlikely but sound fun" is actual competition, where players match up to write characters the fastest from a set list in a multiplayer game.
Following in the vein of games, for people who want to just read characters, you could have something similar to Kanji Invader ( http://tell.fll.purdue.edu/JapanProj/KanjiInvader/KanjiInvader.html ) where you type the pinyin for characters or character phrases to make them explode à la Space Invaders.