Hahah, I'm thinking of all the weird things you could do with that. Imagine writing in "WATCH OUT FOR THE GROUNDSKEEPER'S DAUGHTER" or something like that, when there in fact is no groundskeeper. Or a daughter.
Ooh, and a variation on the "limited characters" thing could be limited space. Having just 5x4cm to write / draw on, or something - it'd lead to some interesting compressed messages.