It's been nearly a year since CIII, believe it or not. A Celebration IV seems almost a given, and the consensus is that it should be in 2007 since that's the 30th anniversary of ANH, the 10th anniversary of the Special Editions, and the year the Clone Wars toon series is supposed to come out.
Nothing has been confirmed yet, but there've been hints. And two recent stories on SW.com have mentioned an "anticipated Celebration IV event"--and as the official site, they wouldn't mention something like that, even in an offhand manner, for no reason.
So who's on board? I know I am. CIII was the highlight of my time as a SW fan thus far. One of the funnest things was getting to meet VIPs and people I knew online from various sites. I'd only started posting here at JD a few months before CIII, and spent most of the time in the MN forum, so at the time I only knew a couple of you outside folks. I'm looking forward to meeting many more of you next time!
I just wish they'd announce details soon, so I can start making plans and saving up.