I've recently started using Last.fm. I made an account a while ago, but I never used it; I thought it was a little awkward to use, and I didn't totally understand how the whole thing worked. My initial thoughts were, "I don't want to have to manually add every band I like, and I don't want to have to listen to a single song at a time!" But, this is because I didn't understand anything about how it worked, or it's purpose. All I thought it was was a way to look at one song at a time; how wrong I was.
So, when I revisited it yesterday, I decided to take a better look at what was going on. I went to a band I liked (Franz Ferdinand, to be specific), and tried out the "Listen to Franz Ferdinand Radio" button; and this is where everything totally turned around for me.
Last.fm began picking songs from a group of similar artists tagged by other users, playing more similar artists more often. Within an hour, I had listened to about 15 bands I didn't even know existed, that are now some of my favorite bands. The real power in Last.fm- at least for a casual listener- is in this, finding new music. For a while, I had been waiting to hear new songs on the radio that I enjoyed, and then trying to track down a copy; and then, I would listen to it until it burned out and I was totally done with it for another year. Now, I can listen to a variety of music that I'll probably like (and if I don't, I can always skip it), and it'll take an entire genre to be burned out before I run out of fresh music to listen to.