If the historical charts are anything to go by, I would say we are in for another drop in prices but at a slower rate than we have seen this last 18 months. I am guessing on another 10% to 20% drop by 2012.
Reasons for my thoughts include another wave of problems with bank balance sheets starting later this year, Lenders are still not handing out mortgages, much higher unemployment to come yet, still a fair possibility of higher interest rates and if the 3.5 times earnings limit is strictly adhered to then prices will have to adjust to meet those levels unless we see first-time buyers suddenly start pulling 40% deposits out of thin air.
If we get through the rest of this year without the economy taking another turn for the worse and the original proposed QE amount of £150 Billion is not exceeded then I would accept a 50/50 chance on the end of falling house prices.
House prices never seem to recover in a straight line either, and normally do not see any real recovery for 1 or 2 years after the end of a recession.