Pandora allows you to "seed" artists or songs to a radio station. This means that station will play all songs related to that artist or song as well as the original artist or song the station was made from.

You can check your own seeds and stuff by going to:

http://www.pandora.com/people/<your_user>

You can see all your stations, your likes and dislikes, and seeds. What I've done personal is created a station, named it "My Station" instead of "Artist's Station" which is default, and added like 15-20 artists that I like to the station seeds.

You're not likely to notice much of a difference if you seed similar artists or songs together, but if you seed something dramatically different.. like classical and country.. or rap and alternative or something - then you'll notice it when Eminem plays on your Nickelback station or something.