Itunes user since at least 2003. Consistent library metadata from that time with about 7k songs/80GB. Main iTunes library is on my iMac at home that acts as the media server for the house, and all idevices sync to it (2 phones, 2 iPads, assorted older iPods). The iMac is connected directly to my high-end headphone system and also distributes music and content around the house via AirPlay. I also subscribe to Match both for portable devices and to have access to my entire library from my work computer.
As I say, I'm extremely picky about metadata, so I've always used the basic list view. Match doesn't do a good job of keeping that in sync, but otherwise I'm very happy with the service.
Itunes 11 was a big shock at first because so many things I'd done for so many years were changed or removed. Overall it's not a huge step forward, but I'm basically ok with it. Turning off the Search Entire Library option went a long ways towards making it usable to me. I do now find myself using the Mini player at work, which I never used before, because I can now rate songs, see what's coming next, manipulate that list, etc. I also use the album view because I find it better than coverflow ever was for scanning my library, and the graphical view still gives me access to most of the features I'd want.
I think the loss of some things is odd - the ability click on the status bar on the bottom to change the detail view, find duplicates, loss of album art in Songs view, etc. But I also know that most early reactions to change are extreme, so I'm willing to work with it. I've found a bunch of positives and only a few negatives so it's overall a slight net improvement for me.