I have been using DMSA for going on two months now. I am currently up to 50mg every two hours, and I may go higher (Cutler says you may go up to 1mg/lb of body weight).
No problems to report so far besides a stiff neck every time I am on it (which tells me that I must have accumulated metal the neck area that is being pulled out).
I am going to ask my naturopath this week if he knows of any doctors who will prescribe DMPS, as I want to try alternating rounds of DMPS and DMSA.
As far as chelating heavy metals with diet alone, I wouldn't count on it, unless you are fine with chelation lasting decades (if it ever even happens).