I'm a D.O. and a OMM fellow and will begin my PM&R residency at Mayo in 2003. It's a great field, but $700K is definitely the top 2% of earners in rehab. Most of the physiatrists doing sports, spine, pain, occ med, electrodiagnostics, and musculoskeletal kinds of practices are in the 200K neighborhood. Plus, many physiatrists become partners in ortho groups, medical directors of rehab units, co-owners of outpatient rehab facilities, or imaging centers. The typical (non-business minded) physiatrist does a little better than primary care---$140K or so and probably mixes inpatient and outpatient practice.
That said, we're talking about a specialty with minimal call (ever hear of a rehab emergency?), low malpractice (unless doing interventional stuff), and all-in-all a great lifestyle. I know few physiatrists working more than 40-50 hours per week.
One of the nice things about PM&R is that you can set up your practice so you get out from under the thumb of the insurance companies by doing sports medicine, performing arts medicine, occ med consulting, manual medicine, disability work, medicolegal work, etc.
I think up till now it's been one of the best kept secrets in medicine. Things are changing though, the last PM&R match was one of the most competitive in recent history and top programs saw increases in applicants of about 15-20%.