I personally would feel it a better idea if you did it after your BS degree than the PhD because the PhD already puts you at a disadvantage as far as getting an ordinary dev job and the year off makes the skills more rusty for the specialized high level stuff you might have done in the Phd. But that ship has sailed.
However, that said, if you can time it so that you return to looking for a job around the same time that new grads are also looking for entry level jobs (because companies tend to cluster their new hire job hiring around the times when entry level people become available), you will probably be fine but it may take longer to get that first one since you won't have the resources of your university helping you (like the interviews at school job fairs earlier in the semester)
However what you might want to do to make things better is to work on personal projects or open source projects during your year abroad so that you can show your skills have not gotten rusty. You might also want to plan to be able to handle at least 6 months of unemployment after you return form your trip. You could also consider freelancing which can be done remotely. So you could schedule yourself to work at projects 2-3 days a week and tourist the rest of the time. You would get some experience, you would keep your skills fresh and you would still be able to tour around the world.
You could also consider looking at some of the big companies that hire a lot of grads each year and get an offer and ask them if they would consider holding it for the next year. This won't work with small companies but it could with a large company that always hires every year.
You will get that first job eventually but it may not be the best job ever since you will have some negatives. But so what, get good experience in the first job to become more marketable and then move to a better company, you don't have to stay at that first job forever.
Once you start working, taking a year off to travel is harder, so I'd say go for it. I wish I had.