First of all, it looks like it supports no bookmarking mechanism, and certain features are just plain inaccessible from the main interface. For example, how do I view the Movie Trailers from iTunes, without going with Safari to apple.com/trailers and clicking on a link first?
After I do get into the trailers store, it looks like it's impossible to do any kind of text-based search for the trailers! Bah, seriously, no text-based search? Only looking through the categories? In 2009, from Apple? Gimme a break! Even their trailers web-site supports text-based searching!
After I finally find the trailers I wanted to see, by browsing through the categories, and select to download the ones that I want to see, they download, but I cannot play any trailer whilst it is being downloaded. Seriously, playing movies as they are received on the wire is supported even from the browser, so why do I need a separate media application that cannot do this simple task for me?
Anyhow, so I go back, browse around. Guess what -- the Downloads tab no more, and now I have to go and find the downloaded trailers in the Movie Trailers tab, which has a lot of old downloaded trailers already. By default, no option is provided to sort by date, and it is not sorted by date, so you have to go into the menus to get the Date Added column.
IIRC, my experience with the iTunes U store has been similarly dismal.
I'm totally amazed how a company as praised as Apple can have flagman products as poorly thought trough as iTunes, with the major release number as high as 8, as in, iTunes 8.2 on OS X 10.5.7.
P.S. The other day, something related that I've found, regarding a similar situation with AOL, ironically, written by someone who works at Apple: http://www.stuartcheshire.org/rants/AOL.html .