I made a pretty drastic career change: Went from being a civilian sitting behind a desk 8-9 hrs/day designing/building an airplane (4 years doing this), to being in the USMC flying jets for a living.
I was comfortable at my old job, but didn't make good money ($45k as an engineer is not good money) and had $100k in student loan debt (not to mention CC debt on top of it). I had a roommate who was a go-getter and was always bettering himself and making things happen in his life...he told me about his "rocking chair" test; when you're 80 sitting in your rocking chair and you look back on your life, what will you regret NOT doing? So, I looked into it and found out I was a pretty good fit for the Marines and made my move.
That was August of 2008. August of 2011 I flew a $28million tactical jet solo for the first time. I always felt pretty accomplished in my old job and like I contributed a lot...it was NOTHING compared to what I do now. The sense of accomplishment is 100 fold.
All told, my move was for the better. Awesome job, the pay is much better (when including all the benefits, etc), they're paying down a large chunk of my student loan, my wife and I are 100% cc debt free, and oh ya, I met my wife because of the change!
Drawbacks: I study/work 10 times harder then I ever did in HS or college, I have life stress unlike any I've ever felt before, I haven't snowmobiled or hunted in 3 years, and I live 1300 miles from my wife, for the foreseeable future...
and all that is washed away when the engine lights-off on startup...