Bringing a bit of a counterpoint to the BaT love....
As many have stated, there are of course both good and bad cars on BaT, and "in general" the whole idea with an auction is to try to get two (or more) people into a bidding war, loose their calm, and overpay. There is a reason there is an economic theory called "Winner's curse"...
Many cars on baT are today sold by dealers, so there is limited true owner interaction. I much prefer to have the contact with the prior owner, you are buying the owner as much as you are buying the car.
In my experience it's harder to arrange a test drive, PPI etc on BaT than on a normal for sale ad or website. Simply because there is the artricifically created sense of "short time". I have yet to buy a car on the site (after trying on a few) and really don't plan to do so unless it's a local car. And almost every single car that is for sale there is also for sale at a normal website.
That said - I will sell cars on the site. The same things that work against you as a buyer clearly works for you as a seller. As long as you are willing and ready to deal with all the comments and (many times) irrelevant and pontificating statements made in the comment field.
As Vander states above, listing a car WELL on BaT is a lot of work.
But, to be truthful - I love browsing the site! Easiest place on the Internet to loose a couple of hours of your life! Love that part of it.
And then there is Cars and Bids, more focused on newer cars (80s forward) but basically the same thing as BaT.