I really like the Trek 520. I replaced the saddle with a Brooks B17 and the rear rack with a tubus cargo rack (though this needed a little work to get it to fit and there may be better alternative racks) everything else was stock. I did a one month tour from Vienna to Amsterdam along the rivers. Mostly the roads were good though there were some gnarly portions (deep loose gravel). The bike performed excellently, no mechanical issues and only one flat tire near the end of the trip. I really like it and wouldn't mind buying again. If you look in the touring forum the darling (as I can see) seems to be the Surly LHT partly (as I understand) because it's customizable. Other complaints about the Trek 520 is the gearing is too high, and many replace with a lower gearing for those steep mountain climbs. I think eventually I will do this, if I ever get around to those alps (they're calling).
Anyway the Trek 520 is a highly regarded work horse, and I don't have any real complaints, just keep in mind this is my first touring bike and my experience and wisdom in this area is limited. Do a search in the touring forum and you will find TONS of info!
Seneca
@BCRider yeah I will bide my time and keep my eye out for a good deal, I do check Craigs list and if I can find a "steal" then I'll go for it.