I've used Pandora Radio on Roku for about two weeks now and I really enjoy it.  I've searched for other reviews on Pandora and people have stated that Spotify and Slacker are better.  I have not used those services because they are not on my Roku device and sound doesn't work on my computer.

Pandora works by you putting in an artist or a track to create a channel.  The channel then plays music based on those preferences.  I started out by a Taylor Swift Channel and it played songs by Colbie Calliet, Sara Bareilles, Carrie Underwood, and Rascal Flatts.  I love Colbie Calliet and Sara Barielles but don't really care for the last two.  Fifty percent right is pretty good!

As I gradually gave thumbs up and down to the station.  The station rapidly changed to fit my interests.  Soon however the station began to play a very limited range of songs.  Some take this as a knock against the Music Genome Projects' ability to find songs you enjoy.  I think the problem is that Pandora has only 900,000 songs in it's database.  Once you've narrowed down your music tastes to a specific set of genes, there are only so many songs that fit those genes.

It wouldn't even play all the Taylor Swift, Colbie Calliet, or Sara Bareilles songs.  One way I found to combat this was to click on the add variety button on the website(not available on the roku player) and manually add Colbie Calliet and Sara Bareilles as artists to use when generating music play on this station.  When I got further frustrated with the playlist, I clicked the add variety button again and added individual tracks by the artist that I hadn't heard before.  Even adding tracks that I had thumbs upped helped likely due to the way the Pandora Algorithm works.

People can sometimes thumbs up or click add variety on music with widely different genes.  If you have a station with Miley Cyrus and Barry White it'll sometimes give you songs like Miley Cyrus and sometimes like Barry White.  The reason I think adding tracks you've already thumbs upped to the add variety helps even if they're very similar to the genes of the channel is that every track has unique genes and those unique genes will lead to Pandora presenting you with new tracks.

Many people don't like the six skips per hour limitation.  I like this.  It forces you to listen to songs that you give thumbs down to.  I can't count how many times I've given a thumbs down to a song initially only to give it a thumbs up later.  Also, it doesn't really bother me to have to listen to a song I don't like one time.

If not enough new songs are coming up on Pandora I'll take the opportunity to go the website and click the add variety button.  Sometimes I'll just be patient as the longer you listen to Pandora in a single session the more new songs it'll tend to come up with.

Pandora is intended to be a music discovery engine however the engine seemed to favor already popular songs and artists. Surely obscure artists have pop genes?  It should be noted that William Hung and Rebecca Black are available artists to select.  Tay Zonday is not.

Pandora has some bugs like skipping and not playing tracks probably.  Unfortunately this tends to happen with tracks you have not listened to before which compounds repetitive channel problems.

One issue with the Music Genome Database that I don't know if Pandora deals with is that people tend to like famous artists and perfomers.  People might give thumbs down to artists just because they don't know who they are and automatically assume they like tracks because they like a particular artist.  Not all artists use the same vocal style in all their songs.  Their are several vocal modalities within the same artist: fry, falsetto, head voice, mixed, etc. and then there's the tessitura where the song falls into.  Artist bias may confound the music genome's ability to ascertain your preference. 

Another issue is that you are exposed to a lot of songs outside of Pandora like in the mall or the car.  I used to love Kelly Clarkson, Katy Perry, and Adele but I was so blasted by their songs that I got sick of them and would never thumbs up their songs on Pandora because pretty much all of their songs are hits and there's no discovery to be made.  Adele's early songs I don't particularly enjoy.  Katy Perry has some good early songs like You're So Gay and One of the Boys but I can live without them.  There are acoustic and itunes session version of songs that can lead to discovery but they are not so radical as to freshen up a "stale" song.  The solution is to either never listen to any other radio station than Pandora so you don't have the stale song phenomenon confounding the Music Genome Process or to use the "I'm tired of this song feature"(although it's not available on the Roku and I couldn't find it in the browser version).

The Music Genome Project feature of Pandora is excellent in determining what musical types you like.  The problem is that at only 900,000 songs this will become narrow very quickly.  This tends to lead to a repetitive playlist that may lead to you missing songs you'd love.  This issue will improve over time as Pandora continues to add more songs to its database.  In the meantime, the user can make some adaptations to the issue: really listen to each song before deciding whether to thumbs down, make copious use of the add variety button including adding songs you've already thumbs upped, and record your own albums to submit to Pandora!