Piggy backing on this. I've came to my first real-word-example where a member has exceeded the limit for a visitor message. I've responded myself, and hit this limit. I've obviously made it higher - but it might be neat to indicate (like twitter) how many characters you have typed and to disallow you typing more if limit has hit, or coloured in the text red perhaps like twitter to indicate you've exceeded the limit set.
I'm surprised this doesn't exist as a addon already? Maybe it does and I just can't find it!
This sounds like something @apathy would enjoy sinking his teeth into.