The bug that required people to add text to both the Intro and Extended boxes has been resolved.
Aside from your standard guidelines (no cursing, personal attacks, et al.), the only rule for the diaries is that your entry must be 300+ words long. The thinking behind this stipulation is that anything shorter probably belongs as a comment to a post or open thread. The word limit may be reduced in the future, but we're going to gauge how things are going before making that kind of decision.
So, once again, enjoy!