One way to be sure you're getting on pretty full flights is to book online and check the seatmap before you buy the ticket. (I think Orbitz has their seatmaps pretty close to the front of the process.) There was a great tip story in the Wall Street Journal a few months ago about how to get a decent deal when you get bumped. (The point of the story was that vouchers usually have big strings attached and often aren't worth it.) I think if you search wsj.com, the story is in the premium archives--it'll cost you a couple of bucks to see it, but that could be a good investment!

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