By far the best character on the show. But just a few thoughts.
He "re-lived" certain moments of his life when the hatch imploded, with vague memories. He had an ability to see the future (Locke's speech, Charlie, Naomi). He has been able to presumably change the past in 1996 and visit another time while not time traveling. He has aquired memories from years past.
So, basically whenever you need time shifting consciousness, Desmond is at the ready. We've had many episodes where Desmond was caught in some kind of consciousness temporal-flux thingy (not a scientist so forgive my vocab) Yet every time it was done in a different way. We've seen this consciousness/time shift occur in about four different ways now.
Im guessing the next episode will at least touch on Desmond, but bets are that it's a Desmond episode itself. I'm also guessing that we will see this odd flux thing of Desmond's come into play in yet another bizzare way. My guess? I think he will somehow make a jump, or connection, or bond, what have you, with the FST.
Some have even suggested this has been the case before with our Jesus-bearded Scottish "brotha". In one timeline he stopped to talk to Charlie before it rained. Later we see this scene from Charlie's perspective and there is no Desmond.
I beleive there will be some sort of merging of the timelines, otherwise the FST would be completely pointless. And I think the best possible option to do that would be Mr. Hume. Don't know how, but I bet he's gonna do some FST visiting next episode.
Also, if any of you listen to the Lost Podcast, Damon and Carlton sadi something about Desmond and the upcoming episode you should check out (I won't say here for fear of it being considered a spoiler)
One last thing about Desmond. Has anyone else ever thought Desmond isn't Desmond without his trademark beard and blue shirt? He had that same beard and shirt for a straight two seasons. Without it, his awesomeness fades. Maybe he will now be stuck in his "red shirt" (uh-oh) for the rest of the series.