Plenty of great developers take sabbaticals. Okay, okay, I just quit my job to take 2011 out as a self-funded sabbatical. ;)
But no, seriously, they do.
I've researched this topic a lot before coming to the decision to do it myself, and these are the basic findings: No, it's not a career ending move, but it's definitely a good idea to stay in practice and do something interesting during your gap year. If you take a year off to sit at home drinking beer and playing WoW, and come back and tell recruiters and hiring managers as much, it'll make you look exactly how it sounds. But if you take a year out to pursue some crazy and interesting adventure, and especially if you do something noble like volunteer work digging wells in Third World countries, then you'll be an interesting interviewee. Essentially, it pays to have a "good story" with some productive content, so the gap year doesn't sound like you just wanted to take time off to be lazy and do nothing.
Also, be careful about dropping completely out of practice with programming and technology. It's true that programming is mostly concepts and state of mind (and specific syntax is mostly is just that, syntax), but you still have to be careful not to come back and be all rusty and awkward in interviews. It's probably a good idea to, at the very least, do some refresher work (in the form of personal projects or maybe open source work) in the last couple of months of your gap year. The more the better, of course.
All that said, you probably should expect it to be a bit of a temporary career setback. Unless you have the reputation of a real rockstar programmer, you'll probably have to take a job that's a notch (in terms of seniority and pay) below what you could have had if you kept working and climbing the career ladder during that year. But it definitely doesn't have to be a career-ending move, unless you do all of the above spectacularly wrong.