After using eBay for the past 8 years, Yahoo! Auctions kind of suck. Sometimes, just sometimes, they will have something for sale that eBay doesn’t.
The first thing that kind of sucks is if you enter a max incremental bid that happens to be greater or equal to the buy it now price of the item, it will automatically purchase it for you at the buy it now price. So if an item’s starting bid is $55 and has a buy it now of $75, having an incremental bid of $75 buys it automatically (that’s how I wasted $20, thanks Yahoo!).
The interface also really bad. As a logged-in user it’s really hard to find anything. Want to leave feedback? Not easy to find or centralized like eBay’s My eBay.