The signs are defo there, what will happens next is best guess though, I think Paul Ripley is right though, I was talking to an estate agent friend of mine last night up here who said that they have 3 times the amount of properties for sale then they did at the same time last year, and that's purely due to the fact they are not selling.
I also read an interesting article that says things are still in the early stages, i.e it's not so much that house prices are falling fast yet etc... but that the amount of transactions falling through are on the dramatic increase, which can only have a knock on effect.