It very much depends on whether the home is 1) a foreclosure (owned by the bank), aka REO which stands for "Real Estate Owned" or 2) short sale pre-foreclosure (owned by the home-owner where the owner owes more than what the home is selling for). Banks typically try to list their properties at aggressive price points leaving less room for negotiation. If a home is listed for an extensive amt of time, a bank will have flexibility, Remember, the last thing they want is to own the property. Remember that the terms you give a bank can be more important than the price i.e., cash vs. mortgage, early close dates. On average, I would say that banks are getting within 5%-10% of their asking price and oftentimes over list price if it is priced right. Make sure to do your research to determine what the property is worth. The biggest mistake some buyers make is thinking that the best deals are based upon how much of a discount you get off of the asking price. Some of the best deals I ahve seen this year, buyers have paid full price on an underpriced home compared to other buyers who have received a 20% discount off of the price and paid more than it was worth.
Referring to Short sales, it is much more difficult to answer your question. It truly depends on the value on how low you can bid. Some homes are priced below market value, others accurately, others way too high. Best of Luck! There's great opportunity out there.