How long should I wait for a response on my offer?

[Minna Reid]

I have a strong offer in on a bank owned property since last Monday. I was told the bank has multiple offers, and would be making a decision within the next day or two. a week later and no word yet. Not even a no. The house is still current and listed as available on the MLS. I have a realtor working on it and she keeps leaving messages but no response. What should I do? Just wait? Withdraw my offer? I can't be hung up on this when I could be looking at other houses, but I'll be in a jam if I get multiple offers accepted at once. Are banks always like this?