I just bought a 2006 STI from stohlman.
I can say that the experience was extremely easy and worry-free for me, but part of that is because I am a well-informed consumer with very specific requirements.
The reasons I chose Stohlman are:
-only dealership in a reasonable radius to have the color combination i wanted
-their regular advertised price matched the invoice pricing from cars101.com
So I sent a "Quote Request" on the individual vehicle on their website that interested me and got a reply within a day. I received a call from Eric Asp the following day and we began the process. I specified that I required a car with fewer than 7 miles on the odometer, and he obliged, informing me the one I was looking at had 6. So I placed a deposit.
A week later, I was ready to purchase with a PAL check from my credit union so I called them up, was told Eric was out of the office but Tom.com could help me and they'd have it ready for me the following day by noon. I arrived at the dealership, spent about an hour going through all their paperwork and registration transfer, etc... And drove home.
I Also got them to throw in a set of AllWeather floormats and 10 oil-drain-plug crush rings, since I do my own oil changes. They happily obliged on both.
I'm not really sure what else you'd look for in a buying experience - I was totally pleased with the whole thing.