mergers and acquisitions. I was on both sides, but more so on the side of the acquired and I suffered. You never want to be in accounting/finance of the company that purchases you as you usually end up without a job. I've lost a job 5 times because of it and in each situation, when I went to work for the company, everything seemed in order. I started my current job with the notion that the owner wanted to sell in the next 3 years. To my surprise, that "next 3 years" ended up being 1/2 year later, but everything has been fine so far and I don't have any reason to believe it won't continue until I retire in 3 years.
So, just really try to make sure where you are going that it is firm. It sure it's fun to be getting great reviews and then suddenly you are shown the door because someone else owns the company.