i was a CNA for 2 years before i started med school. there are some serious advantages and also some serious nasty parts.
on the up side, the pay is good (i worked in long term care - $15.50 and times 2.5 on the holidays!!!), you get an awesome experience with the patient/caretaker relationship, med schools just love it.... every school i went to wanted to talk to me about it.
but....you are changing adult diapers, bathing and dressing adults, etc. i have been crapped on, puked on (some of it hit my face), pissed on, had more food than i care to remember poured all over me, i dislocated my shoulder rolling an obese patient, and i emptied wound drainage bags (meaning 'filled with puss'), and worse yet colostomy bags.
BUT, i wouldn't trade my experience for anything. the training was relatively easy, and sometimes nursing homes will pay for it if you agree to work their afterwards. its a job that is in high demand, so you don't have to worry about finding work, and it is pretty flexible with school/other work schedules.