I have to admit that listening to last.fm is a completely different experience. There are a much deeper selection of tracks and I was thrilled to hear a 24 minute DJ Shadow song.
I wish pandora the best, and I was ok with the occasional video ad. But every time I change a station? If it was every 3rd time I might have put up with it.
My main complaint with Last.FM is that it makes me putting a label on what I like in music, and then match that up with how other people label music. I know next to nothing about music, I just know I like certain songs and dislike others (Ok, I know a little more than that, but not much). When I used Last.FM I would pick a genre/tag I liked/artist, listen for a while, and get bored with it because it either sounded exactly the same or else I picked the wrong tag and it turns out that wasn't the factor in the original music I liked.
Also, I use Fire.fm firefox last.fm toolbar which is great as it puts play controls right into firefox and last.fm does not need to be open!
Except in other countries than the United States, United Kingdom and Germany.