My vote is on:
* migrating the 34,000 members in an opt-in way [Editet after Milhouse's post]
* starting clean (empty forums)
* starting w single sign-on

Additional thoughts:
* timeline: between yesterday and publish of MeeGo sources (this being the proper milestone for starting karma whoring and a good homepage which appeals to end-users and device manufacturers) I think at that time there could be a new peak in interest (the meego story producing the first real, touchable output), so better be ready by then.