I should point out for those of you who haven't been involved in my more-combat-heavy game, that I haven't been bothering with initiative in my PBP games (actually I've been trying it out in my IRL games since doing it here, but that's another story).
I just resolve in an order that sort-of goes 1: By Post, 2: What makes sense, 3: On my whim, and 4: With the enemies being "activated" by interaction with the PCs or 5: enemies dispersed throughout, as makes sense.
It's worked pretty well so far. If there ever was a conflict, I'd use an Initiative roll to determine what happened first, but it hasn't been necessary yet.
(That's all a long way of saying, go ahead and post your turns in a surprise round)