I won 50,000 AA miles a couple of years ago. There's another thread started recently by someone who won 1,000,000 miles.

As for the tax issue, Travelocity has a contest out right now where they're valuing the miles at $0.01/mile - I'm saving a printout of the rules in case I win something and need to reduce the sponsor's 1099 (I'm an optimist - what can I say?)

Some of these contests have been easy to enter - less than a minute of time invested. As for the spam issue, I use my spam e-mail account (not my main e-mail) for these contests.