I'm doing this one for a new acquaintance who messaged me over on Facebook this morning.
Pete Warden has a Facebook app he's put together called "Event Connector". It's basically a widget that announces to the world that you're going to some event and will compile a list of friends and friends of friends on Facebook who have also stated their intent to attend the same event. You can also place the widget on TypePad and Blogger blogs.
I don't yet see a payoff in mainstream conferences (although certainly niche tech and social network events should be all over it). But it would be a boon for local and regional events near universities or those that target students or recent grads most likely to be Facebook users.
And yes, that would include consumer shows.