I stream everything mainly as background music, and don't have time/patience to sit and program playlists or pick albums when I need that kind of background music. Pandora is on 2-3 hours per day in the kitchen on one of my "trained" stations, and they have enough seeds and thumbs up/down votes that it would take hours before I'll hear any repeats. They aren't a fixed playlist, as I usually hear something new and different each time I use it. I have several of these stations now.
My "70s Soul" station was kind of interesting last week. One day, it played a string of music for an hour that I'd never heard of, that I liked. Mostly mid-tempo stuff. Then the day after, it got into a weird funk (no pun intended) where it started playing some modern day crap--a few thumbs-down smackdowns had that removed in a flash. I try to train this one towards a handful of artists and the 70s Philly sound, and it is doing fairly well.
My "Salsa/Mambo" station is a strange mash-up (if you know Latin music), but it's nice because it will shift between mambo/cha-cha from the 50s and 60s to salsa and boogaloo. I'm always hearing something new on that one, even if I play it daily for several days in a row.
Just randomly picking something isn't going to cut it, to get the most out of Pandora. But I have long felt the training is worth it. My oldest station dates back to 12/14/2007, with one seed artist, 145 thumbs up, 84 thumbs down. My 70s Soul station has eight seed artists and one seed station (Pandora's own "70s Funk" station), with 68 thumbs up and 127 thumbs down. Salsa/Mambo has three seed artists (Eddie Palmieri, Perez Prado, Tito Puente), with 60+ thumbs up and less than 10 thumbs down.