I registered for the (Free) Expo only pass but at £500 a day it's too rich for me to go to any of the talks. It's on about 15 mins from me in London so I'll definitely head over one of the days and take a look round the Expo hall, see who is there (maybe sneak into a talk.)
I might also go to the after party which Dave from Redfly seams to be sponsoring
LondonSEO.org LondonSEO Party - Thursday 21st February
Dave is probably your best bet to see which are the best talks there. To me most look good I think I would go mostly for the talks in the "Search Advertising Track" but there are few of the "Organic & Beyond Track" I would not mind seeing too, the one on "Images and Search Engines" springs to mind as a possible interesting one.
edit lol beaten to it by dave