As others have said, it really depends on the auction. I won a no reserve auction last month at a price that was well below where it should have been. I was high bidder on a couple of others that didn't meet reserve, but couldn't make a deal with the seller.
Their listings are very Porsche heavy, but that's because they're the hot commodity at the moment. Trucks are also very hot on there right now- and not just the one's you'd expect. I saw a basic 1990 2wd, automatic, regular cab Toyota bring $30k!
I like some of the oddball cars that you see on there from time to time. I was bidding on a super charged, 4 speed, Studabaker GT a while back. It ended up going just a little over the max bid I had set for myself.
As for the commenters- some seem like they must spend their entire day just commenting on there. Lots of junk comments. Some are funny. Some are interesting. The ones I don't like are the twats that demand more info or pick a car apart with absolutely no intention of bidding.
Below is my "bargain" Lotus Excel that I bought through BAT.
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1966 GTO
1969 Lemans Convertible- F.A.S.T. legal family cruiser. 12.59 on G70-14 Polyglas tires. 1.78 60'
1969 Bonneville Safari- cross country family cruiser. .
1979 Trans Am 400, 4-speed, 4 wheel disc.
View from the drivers seat racing down Atco Raceway-
http://www.youtube.com/watch?v=GhYDMdOEC7A
Ride along in the other lane-
http://www.youtube.com/watch?v=mIzgpLtF_uw