My son's orthodontist has his office standardized on Macs. He'd always used them for 3-D rendering in the 'back room', but switched the front-office over about two years back.
My best friend's dental practice is 100% Mac based using MacPractice Dental (also available in MP-Medical, MP-Chiropractic, and MP-Optometry). He has nine networked OS X Macs... plus two or three at home tied in with VPN.
A Chiropractor sharing the same building, fed up with Windows problems, is seriously considering switching to Macs. Several of my clients are optometrists who are also talking about switching.
Other users of Mac computers: Shimmer
My son's orthodontist too.