Success! After much fiddling, i've done 75% of what you guys want/need.
Typing "/" will make the rest of the message untouched by the punctuation changes.
Automatically makes the letter after a space after a "!", "?" and "." a capital.
(ie woot. i rocks! yep!
becomes
Woot. I rocks! Yep!)
Automatically ends any open-ended sentences (ie, without any ending punctuation) with a full stop.
All that jazz...
Except, i cannot configure it so that it ignores messages starting with "www." "http:" etc...
http://pastebin.ca/77236
By the way - i mostly used the guy a few post up's code, but tweaked it a bit.
edit: It does affect custom emoticons, unfortunately, but only if its the first character. Just press space before entering an emoticons.