I would say hell no. Way too much of a hassle--it kills all of the "be able to travel at moments notice" and "be able to up and move quick and easily anywhere" ideals presented in this thread.
I just got a cat and would say the above applies to cats as well but less so (I recognize the hassle and probably wouldn't have actively gone out and bought a cat, but in my situation I ended up with a cat and I like it). For instance, I left my apartment yesterday morning to go to work and got home just before midnight. Cat was like "sup?"
Dog would be like "*slobber* *slobber* oh btw, I pooed in the corner."
If I want to go away for the weekend, I just gotta get somebody to stop by over the weekend and check on it (not hard when most of your friends live in walking distance of your apartment). I think most of my friends would be unwilling to dog-sit and I would get stuck paying for a kennel. I could even get one of those sky-mall style multiple day food dispensers and not have to worry about anything other than a nasty litter box.
Of course, if you have a roommate who is not also a close friend (that is, if you are travelling...they probably won't be coming with), then pets might be more of a non-issue but otherwise they can be a hassle.