Advice for Surviving a Buyout?

Anonymous for Good Reason asks: "I'm working for a small-medium sized software company that looks like it's going to be bought by a much larger company. We (employees) aren't being told anything yet, but the behavior of our management and some of the information we have been asked to provide all make it pretty clear that somebody is going through due diligence and trying to close the deal. How have other people fared during these kinds of buy-outs? What did you do to make sure you kept your job and weren't RIF'd after the dust settled? How did your stock options, pay, benefits, etc transfer, and was there anything you would have done different to protect yourself? Was the cultural change a problem, or were you welcomed warmly into the fold? I'm mostly interested in stories from people whose companies were bought by the really big players (IBM, MS, Sun, CA, HPaq, etc.) since that's what this will probably be. Since I have never been through a merger of this type, I'm not sure what to expect and with the current economy I would like to increase my chances of staying employed. Any insight the Slashdot crowd has would be interesting."