I've installed the latest iTunes and began to use iTunes Radio. It seems that my fears about iTunes Radio aren't quite true (and my fears for Pandora are realistic). iTunes Radio initially presents you with a list of stations that are presumably human-programmed, but you can also add your own station based off of a genre, artist, or song (similar to Pandora).
Here's where it's actually pretty neat. There's a slider that has markings for "Hits," "Variety," and "Discovery" (and you can set the slider to anywhere in between the three). Presumably this is what controls how "faithful" the station is to your base selection. If it works as I think it will, this is something that will make Pandora seem archaic. There are times when I want to hear something new, but there are times when I just want to listen to a mix that I've become accustomed to. With Pandora, breaking out into something new by adjusting your song ratings can adjust the character of the entire station. Bravo, iTunes Radio.
iTunes Radio doesn't use the "thumbs up/down" rating system, but it has similar functionality. Clicking the "star" icon brings up the options of "Play more like this" and "Never play this song" (there's also a third option for adding the song to a wishlist).
There's a nicely-displayed history of songs that were most recently played on the station (which seemingly remains in-tact even if you close iTunes or listen to another station and then return to the original station later). The song price is displayed here, as well as in the pane at the top of iTunes (where song progress is displayed). If you already own the song, no price is displayed.
Lastly, Pandora One users who used the Pandora desktop application may remember how Pandora One would display the song artist and title at the upper right display when a new song began to play. As an Adobe Air application, that notification wasn't based on Growl or OS X. iTunes Radio uses a similar notification, but it works through OS X's built-in notification system. Very, very nice. (For the curious, the currently playing song appears in the Notification Center, but the song history does not.)
As of now, it seems as if iTunes Radio is what I had hoped. It appears to have similar functionality to Pandora, but it makes purchasing music much more accessible.
Good luck, Pandora.
