I've been a paramedic for 13 years and am now a first year medical student. I wouldn't trade my knowledge and experience in EMS for anything.
I find that my clinical background has been invaluable so far in relating the sciences to real world clinical medicine. It keeps me focused and helps me learn. It has been incredibly helpful in my PBL sessions where we solve clincal cases. I am also convinced that this experience is what got me into medical school. Finally, I absolutely LOVED working as a paramedic. I think it is one of the best jobs I can think of. I'd gladly recommend it to anyone who wants to make a contribution to the field and to patient care.
However, I strongly echo what Kimberli said early. If you are just doing it to get into med school, save yourself 2 years and save EMS from another person who really doesn't have their heart in it.
If I can answer any questions for you, please don't hestitate to ask.
Take care,