Something we’ve noticed and annoyed by for years now is iChat (and likely other instant message clients) tends to throw up when you try to send code through them when connected through the AIM network. Specifically, HTML or text with < and >. There doesn’t seem to be a lot of rhyme or reason as to when it happens, either.

One little trick we use when in the office is to open the Bonjour List (⌘ + 2) and send the message via Bonjour instead of AIM. Voilá, code through IM.