The answers that follow mine are all right--sad as it may sound. And in the present economy, don't be surprised to see the banks which give written approvals may also find themselves in financial difficulties and not be able to perform. EVEN IF THEY HAVE PROMISED YOU THE WORLD IN WRITING. Your best bet is to find a BIG bank or lender, which would be likely to still be in business when you are ready to buy/close on your new home. I'm thinking BoA, Chase or the like.
Today's lending environment has gotten extremely tight and the automated underwriting along with the waivers that came with them are no longer holding weight with underwriters.