Every major airline offers some kind of frequent-flyer scheme, and more than 100 million travelers worldwide participate in them. These programs' popularity is no surprise, given that the bulk of them offer attractive rewards for members who know how to leverage their miles. However, to maximize the benefits of frequent-flyer membership, it's important to be aware of the programs' pitfalls. So we spoke with an expert, FrequentFlier.com publisher and SmarterTravel columnist Tim Winship, to get the dirt on everything from upgrades to surcharges. Discover the 10 worst things about frequent-flyer programs, and find out what travelers can do about them.