Nothing, really, and a lot to gain from a technical perspective.
As I said, I'll be leaving this forum here--I'll just lock it down.
And for anyone who's wondering, if you're just after a quick and easy forum with minimal maintenance, Proboards is good, and I'd still recommend it, in spite of my complaining. Yeah, the ads annoy me, and the fact that a lot of things I think should be free are pay only seems a bit greedy, but the service has actually been pretty good.
Well, except for the built in live chat engine. That thing never did work.