I'm over the limit. This is because I buy music from iTunes and these songs are not included in your quota. Currently I purchase around 30% of songs from iTunes. The other 70% come from other music stores (www.bandcamp.com, www.traxsource.com mainly), rips and gifts.
The problem is I do not know what my actual limit is due to iTunes not telling me how many more non-iTunes sourced tracks I can add. Thus I'm having to make decisions about which tunes I add and which albums sit in my dropbox never to enter iTunes.
So now I have a 2 tier music library :(. I can't even play the tracks in my dropbox via iTunes as it will auto import them on first play. I know I can disable that feature but that would also mean iTunes would stop keeping my folders organized and that was the reason I started using iTunes all those years ago.
Wish Apple would remove the limit entirely and just charge for storage. It makes no sense having a cap like this as it doesn't encourage you to use iTunes Match it hinders you.
In any case even if you where Kim Dotcom your library cannot be shared (downloaded) by anyone but the owner. Sure you can share the library so everyone can play the tracks but that's surely something Apple would want to promote.
For now I'm making this decision daily... play in iTunes or store in dropbox.
I don't want to think.