I sold a 2 year old powerboat on eBay, got the "buy it now" price in 15 hours. I look at the eBay boat auctions often, and it seems to me that as far as sailboats go only the smaller cheaper boats actually sell. I think many people are just "running it up the flagpole" with the bigger boats; it's only $40 to list any vehicle. There was a spectacular S&S Tartan 46 on there about a month ago that got a bunch of comments and questions but no bids, which is sort of typical. I think people take one shot on eBay, if it doesn't sell then it's time for a broker.
That said, what worked for me is lots and lots of photos, and a very detailed listing (synthetic crankcase oil changed every 50 hours, etc.) Pretty much the same stuff that catches your eye on Yachtworld.
It also didn't hurt that some guy was looking for a boat similar to what I had listed and got outbid on one a week earlier.
Anyway, that's my $.02.