For me, I feel like buying from the market wards isn't terrible (yes its not as quick/easy as an auction house, but im not ripping my hair out over it). What kills it for me is selling stuff on there. That is the real problem/hassle. Basically you have to:

1.Choose the item you want to sell from your retainer
2.Exit that menu and go to the search function
3.Figure out what category the item even falls under
4.Look at the prices of the item
5.Exit those menus and go back to retainer
6.Put the item up for sale

Now with a good UI based auction house they could reduce that many steps way down. Type in the item in a search function, check prices, put the item up for sale, done. Right now theres just way to many menus to go through just to sell 1 item, and with the UI lag, its really a hassle.