While iTunes is clean and easy to use, it's also pretty sterile. If you know what you want, you'll probably find it there, and you can buy it very easily. You can even get a sort of automated personal shopper in the form of the new Genius feature. But unless you have a friend sitting at your computer with you, shopping at iTunes is not a very social experience.
Those who desire more of a human element in their pursuit of online tunes can go to music social networking sites like Last.fm.
However, music social networks can be pretty small and fragmented. Most users will probably find that only a few, if any, people they actually know are members of the same site. So when you want to find new stuff, you're still taking recommendations from either a) the few friends you have on that particular site, or b) a cold, heartless database with no actual taste of its own.
