Another problem my wife and I have run into is lag time: there is a delay between posting things in the MLS and then onto the internet sites. That delay is usually the time it takes for the better deals to have an offer pending on them. Even though the UI of the "official" MLS site that our agent uses sucks compared to sites like zillow and movoto, you can find the cheaper houses before they go pending. Too bad there isn't a filter on the "status" field in the MLS web search (such as, filter out the 1/2 to 2/3 of houses that are already pending???)

That said, Zillow is a wonderful tool to check price/sales history.