You know what I hate, deep within my soul? The way they handle the "vintage" category. Instead of making it just "before x date" and "after x date", they will have a general category, then a vintage category - which means 50% of people will put them in the vintage, and 50% will use the general, meaning I have to comb through the listings twice. Well, thats just two searches, not that bad, right? Well, if it just so happens the item is still being sold wholesale, like, say guitars, the answer is big flipping "no", because you will have to search through hundreds of retail and second hand new guitars to find that old Tele. And so much for using that trusted "email me when this item is available" option, because you'd get sent hundreds of emails weekly, telling you about crappy new Telecasters. They do this in many other fields, including video games. This also totally sucks if you're selling, because if somebody is searching through a particular field, unaware of the other, they'll miss your item. Of course, you can get listed in both for more money.
The whole sorting system sucks in general, full of either too vague or too specific categories, the whole thing's is terribly managed. It's just like Microsoft, get you self into absolute power then avoid any real effort to improve your product, because you can.
Oh yeah, they also like to occasionally hide the most useful feature on the whole damn site - "Search completed items". Every now and then, they'll change things around and hide the darn thing on you. Even if you hate eBay, that ability to immediately find out the real world value of nearly any secondhand item is absolutely indispensable to anybody that buys or sells anything collectible or second hand. No, lets hide that guys.
You should be use to it by now!