I've bought my last 2 cars off the internet and it was a really easy hassle free experience. I used zag.com both times. Let the dealers battle it out, pick one you're happy with. No need to go into the dealership, that's what a phone/email is for.
I was there maybe an hour to pick up the car. Of course they try to sell you the extended warranty and other stuff but they didn't push. A simple no and on to the next item.
The first one was a Mini for which the conventional wisdom was that dealers never discounted off of list price. I emailed every Mini salesperson within an easy day's travel with what I wanted to order and had a discounted offer over the phone within 5 minutes - within two hours I had a more convenient dealer match the price and throw in a few extras. First and only time I stepped on the lot was six weeks later to pick it up.
Last car I bought, I found online though AutoTrader with the options I wanted on Sunday about 120 miles away, but the dealer was closed. Called Monday morning 8am, negotiated the deal over the phone by 10am, and the car and paperwork were delivered to my driveway at 6pm that night.