Every market is different. I'd recommend starting to watch prices now, so you can recognize a bargain when the time comes. Also, start watching the supply and demand data. This would be housing supply and absorption rate, which is how quickly homes are selling. Not every market is hot right now. In particular, some builders overbuilt in certain areas and so you might get a better deal there.
Personally, I wouldn't put down anymore than I had to. IMO, the housing market (in most places) is still pretty volatile and if you need to short sell the home you may be glad you didn't put everything you had into the downpayment.