Until I learn how badly their replacement for "iTunes DJ" sucks, I guess I'll put off installing this as long as possible. If they broke the ability for it to draw its choices from a smart playlist, or the ability for anonymous iPhone users to request songs, I'll never be able to upgrade the version that we run at DNA Pizza.
The removal of multiple windows also sounds like it will make the construction of my mixtapes be much more of a pain in the ass.
Since I'll be forced to come to terms with it eventually anyway I'd like to test it out myself, but I assume that, as usual, the only way to downgrade is to restore the whole system from backup, since iTunes gets its claws into everything. Blah.
Update: Yeah, it's not looking good. Ars Technica:
While Up Next seems intended to replace iTunes DJ, it lacks some of iTunes DJ's functionality. For example, there's no more ability to stick to higher rated songs. There was also a related feature that let iOS device users "upvote" songs to play sooner or more frequently. Overnight, these fantastic features have been stripped away.
Another missing feature is the ability to open playlists in separate windows. There's a new dedicated view to edit an existing playlist. [...] But some users simply prefer to have multiple windows open in order to search for various songs and drag then drop them to a particular playlist.