The short answer is very much, "It depends." The earlier you are in your career, the more that a full-time MBA makes sense. After you have about five or six years of work experience, a part-time MBA starts to make more sense. Beyond ten years of work experience, then a full-time MBA isn't really an option (at least not at a top MBA program), and an executive MBA is what may fit you best.
Even for employers, the answer is the same: It really depends on where you are in your career and what you want to do with an MBA. If you want to switch careers, a full-time MBA is your best bet. You'll typically have more access to on-campus career service, can take advantage of the summer internship to prove your self (and to try out) to a new company, etc. If you're further along in your career and like where you work, then you may just want to go for a part-time MBA or EMBA.
Switching careers with a part-time MBA is possible, but for the schools you're looking at, carefully research whether or not you would have the same access to on-campus recruiting that full-time MBA students get. At some schools, part-time MBA students are dissatisfied because they get less recruiting support than they expected, because those programs aren't always built with job-switchers in mind.
BTW, we recently took an in-depth look at some of these programs on our blog:http://blog.veritasprep.com/2010/02/alt ... art-1.htmlhttp://blog.veritasprep.com/2010/03/alt ... ba_25.html
Hope that helps!