No idea whether you're still lurking in this forum, LisaMC, but I'll give you my two cents.
I got a masters degree in paleopathology (or palaeo, if you prefer) from Durham University, in the U.K., in 2006. It worked out very well for me. Masters' degrees in the U.K. tend to be very efficient (one year) and they have some very excellent bio-anth programs. They're also very focused on classics (which, as a mesoamericanist, wasn't so great for me, but would work for you). On the other hand, I didn't get a lot of attention from my advisors nor did I make very many contacts. Lectures are conducted very formally, in my experience, and there isn't a lot of interaction.
Since getting the degree, I've been teaching at community college. I had to pay a company to evaluate my degree and confirm that my international degree was equivalent to a U.S. master's degree before I could teach, but degrees from the U.K. are always accepted as equivalent, as far as I know--it's just a formality.
I just finished the PhD application process and will likely be headed to Penn State this fall. As far as I can tell, a masters degree is treated as a masters degree, whether it's from the U.S. or the U.K. It serves to prove that you're committed to what you're doing. The places that accepted me all claimed to be impressed that I had been willing to go overseas to find the right program.
I will say that I depended heavily on my undergraduate (U.S.) advisors during my PhD application process, rather than relying upon my U.K. master's degree professors. Keep that in mind if you ultimately want to live in the U.S., and do your PhD here. Overseas professors are less likely to have the contacts and be up-to-date on inter-departmental politics.
Be prepared for grim weather and root vegetables. And learn trivia for pub quizzes.
--Diospyros