The official site notes that the convention will host the "official Minecraft launch," despite that all accounts so far set that date for 11/11/11. Given the ground-up nature of enjoying a new world of Minecraft, it seems likely that the team will roll out the final, official update on the planned date, while the panels at MineCon will focus on what people have been able to make with those new features in the week-and-change that follow. (Well, that, and Notch will need time to play Skyrim!)
There's no word yet on what to expect once you're there, other than "keynotes and classes," but the Notch's original post mentioned ideas like speed-building, costume contests, and more. If you're attending, consider packing your diamond sword to fend off the inevitable wave of cosplayers as they interpret what a creeper looks like!
MineCon tickets are going for $99 in advance, not including hotel fare, and will stay on sale until Notch decides the hotel's whitelist has reached capacity.