The good, the bad, the ugly is all part of the fun! I haven't flown on a paid ticket in two years. Admittedly I have gotten stuck twice, and I didn't really want to leave so I gave up sort of easily. In both situations I probably could have gotten out if I actually utilized my back up plans.

In the past two weeks I non-reved on nine flights on four different carriers alone. Was in NRT, stopped at home for a few hours, hopped over to a wedding in SJU, and then met up with a friend in BOS on the way back. I could have never accomplished all that on paid tickets!

It's exciting, can be stressful, but for what it's worth it's an excellent privilege. You just have to make sure you can be flexible if things don't go completely your way.

USA-LON flights are easy. There are tons of frequencies on many different carriers. Choose a city pair with different frequencies on different carriers that are the same (or lower) ZED level. I don't know what agreements WN has, but say for instance AA, BA, BD are ZM, while VS and UA are ZL. You want to fly ORDLHR and all of those carriers operate that flight. If you purchase the ZM ticket, it's a little more expensive, but would be accepted on all of those carriers operating that route. The only caveat I have is that for certain carriers (I know BA for sure, possibly VS as well) if your coupon says LHR you cannot use it at LGW. That shouldn't be a big deal. This example goes for any airport with multiple frequencies to LHR/LGW/etc.

To check loads, just call up the airline reservations number or their non-rev desk. The number that you are required to call should be listed in your agreement with the airline. If it's just the normal 800-number, it's also good to carry around the local number of the carrier in the place you'd be going so that it's cheaper and easier to call to check the loads on your return.

On the leg out, you'll probably be biting your nails, but by the time you land in London you'll be happy you took this route. Enjoy!