I for one will endorse Ulfo's point as I won't waste my time bidding on an item when I know for a fact I'll be gazumped 1 minute before the Auction ends!
I don't even look at Bid Only Auctions as I want the item there and then NOT in 3 days time!
And many of those people who do buy bid only auctions won't even make a bid until there's less than 5 minutes left on the Auction because they're looking for a bargain - So bid only generally hurts the seller because it puts off many buyers and only entices the bargain hunters.