Fab episode... I was doing high fives with myself (as I watched it alone) when Jin reappeared, though I had to rewind a couple of times to check it was actually him!
Theory... the further back in time you first were on the island, the sooner you'll get a nosebleed. So Charlotte was there first (kid Ben went to school with, what was her name?) Miles was there second (baby of Marvin Candle), Juliette is next she's been there three years? That means everyone else is about due for one but maybe not for a while. Faraday should be last to get one since he's spent the least amount of time.
Locke will NOT find out Jin is alive before leaving the island, otherwise surely he would have told Sun (hopefully we find out more about this next week in "The Life and Death of Jeremy Bentham").