I downloaded some random track the other night just to get a feel for the experience. It was slow to download but I assume the transition from such a small pool of potential customers to everyone else may put a strain on a company. That's not really my interest, though as they still contain DRM and I have serious trouble with the concept of paying for a heavily compressed file. The sound quality wasn't bad but it's far from CD quality. If you expect me to pay a buck for a song, it better be a losslessly compressed file.
The player, on the other hand, is a dream. Its treatment of library management is very elegant and it allows me to very quickly find what I want. It only took me 20 minutes to repair all the missing ID3 tags. That said, it's missing some key options that may keep me from using it in the long run.
As to foobar and iTunes playing together, I'm not sure if Foobar supports AAC. While it's built on MP4, it's not MP4 so the ability to play MP4 specifically isn't enough, as far as I'm aware.
