if you get the chance to do this....PLEASE do it!! it was my sole reason for applying to medicine. i was previously dismissing medicine being from a pretty deprived school, i was told i would have no chance of getting in so forget about it...and did...until i went on the summer school in bristol. Everyone else was similar to me, the tutors encouraged me to apply, the whole experience...sampling lectures, socially was brilliant as well...so i thought im gonna go for it...and did, and am now a 3rd year medic in bristol! I would say on top of that it gave me a real advantage in interview, as I had first hand experience at the type of practials they did in bristol 1st year there, and in both my bristol and liverpool interviews they seemed to be very interested in what went on at it, and it backed my reasons up very well!
go for it is all i can say, without it...i wouldn't be sitting here in the hospital library writing this!