I bought my first new car a couple of months ago and negotiated the out the door price completely over email before going to the dealership for a final test drive, paperwork, inspection of the car, and handing over the keys (about 90 minutes total). I highly recommend the method to others.
I got all my details and comparisons at edmunds.com They have forums where people discuss what they paid, what they got and where they got it. You might check it out if you're looking for the best deal.
Notes:
1) I test drove several cars to decide what I wanted to go after.
2) I emailed only about five dealerships.
3) The car I bought is pretty common (2004 Honda Accord V6 coup (leather, power, CD/XM, etc.)), and I'm not sure the email approach will work well without competition (ie. it probably won't work with a Mercedes or Jaguar, maybe it won't work with a VW or Subaru).
4) I bought the car well under invoice and had negotiated the car/options and the "out-the-door" price before going to the dealership.
5) I dealt with one guy. He needed no approval from financing or his manager. He didn't try to add anything to the negotiated price.