Buy.com has to have some of the worst UI I've seen lately at a major ecommerce site (and that's saying something). For one thing, the keyword search form, prominently displayed at the top of their home page, does nothing but reload the home page unless you choose a store from the drop-down list (positioned significantly *above* the keyword input box and the instructions). It took me three tries before I realized what I was doing wrong. Form validation, anyone?