I'm also a bit torn between taking a year out or not. I've started my MSc straight out of undergrads and at the moment I'd like to go back home for a year without having to take airplanes every two months, without deadlines and without endless countdowns (and with lots lots lots of snowboarding!!! youngone I know how you feel!). Also, although I've been reconsidering the idea of American PhD's (5 years, man! that's a lot!), I'm still tempted to give it a shot and in order to do that I'd have to take a gap year.
On the other hand I'd also like to finish my studies as soon as possible, I think I'm getting a bit fed up of student life and want a bit of freedom, and that would probably be easier if I stayed on here at Oxford. The "If you want to do a PhD there's space in my research group" sentence by my supervisor sounds a bit too inviting...I know that I want to do research in my career, I can't see myself as doing anything else at the moment, I know I would love it, and therefore I need a PhD, so it's not a matter or 'if' but of 'when'. Argh, decisions!!
I think fate will decide for me, in the end...I'm try to follow my instincts, apply and see what happens...