If you're traveling overseas, it makes sense to get additional pages put in at a U.S. Embassy. I was in Singapore last month and stopped at the embassy and it was painless. First off, no waiting in line if you're a U.S. citizen; go inside, fill out a short form and hand in your passport. Literally, in ten minutes my name was called and the pages were put in.

Of course, there could be a longer wait depending on time of day or the embassy in question. I was also going to London but decided to pass on the embassy there since it's so large and there are so many Americans in the UK.