Yes, this promises to be a very interesting trip. I'll be flying through Seoul, Korea both directions with a long layover on the way back. I've always wanted to visit Seoul, as I'm a martial arts student and have been studying Kukkiwon-style TKD for the last couple of years...which is conveniently located about an hour (by subway) from Incheon airport. It was an unexpected, but pleasant, bonus to the trip.
So far, every thing has been smooth...it's not the first time I've traveled internationally (I've been to a handful of countries in the Mediterranean a few years back), but it is the first time I'm doing all the planning and paperwork myself. I got a Vietnam visa-on-arrival approval letter, which was much easier, cheaper, and faster to acquire than a Chinese visa...I'll let you all know how it works at the airport when I arrive, but from everything I've read it should be a simple matter of paying the $45USD fee and getting the stamp.