The 52nd Antiquarian Book Fair is at Olympia from Thursday 4th to Saturday 6th June 2009. The opening hours are:
Thurs 4pm to 9pm
Fri 11am to 7pm
Sat 11am to 5:30pm (which is earlier than Saturday closing time last year)
Olympia 2 Hammersmith Road,London W14 8UX
The Bookfair website is here and you can print out a complimentary ticket from here. Ibooknet member Stephen Foster will be there, at Stand 19, which is, he says, about as far from the entrance if you can get.