iTunes 11 has been a disappointingly buggy release. In particular, I've had a lot of problems with both iTunes Match -- a service that, hey, I pay extra money to Apple for, which means it should work faultlessly -- and Smart Playlists. New Smart Playlists would not populate; old Smart Playlists that I count on completely disappeared. Or, rather, the Smart Playlists were there -- they just became depopulated and useless. In the past hour and a half of trying to get things to work and searching these forums for an answer, I mainly heard a host of similar complaints dating back to the iTunes 11's release, with no response at all from Apple about these problems.
In the meantime, at one point the only playlist I had that was populated was the one containing the last 11 albums worth of songs that I've purchased from my laptop (the computer I'm currently using) -- but none of the 4000+ others that I own on my desktop, that are in iCloud via iTunes match -- in spite of the fact that iTunes Match kept assuring me they were all there.
I did find the useful advice from similarly frustrated users to keep on trying. I ultimately got things to work for me -- I guess I'll see how long it will last -- by quitting iTunes completely, then reopening, then turning off iTunes Match, then turning it back on again.
So to other frustrated iTunes 11 users I repeat the refrain: keep on trying, and it will eventually work. At least until the next time it stops working.
To users of earlier releases of iTunes, I offer this advice: don't upgrade to iTunes 11 until Apple works out the bugs.
To Apple, I offer this earnest plea: please fix it. There's a reason that Apple has so many diehard fans: because it delivers great stuff that works beautifully. This release of iTunes is a blot on your reputation. Please fix it. Thanks.