Same for me -- still not working over 90% of the time. I'm in the US.
It works randomly here and there maybe 4 or 5 times a day, and I can confirm it has nothing to do with signing out and back in of my iTunes account, turning iTunes Match off and back on, or turning my machine off and back on. It also has nothing to do with my ISP throttling my outbound traffic. (These are all futile suggestions I've encountered on forum threads.)
To newcomers:
This is almost certainly a problem on Apple's end. They admitted to service outages on Aug. 7, which is when this trouble began for me and others who have posted in this thread, and the issue persists. Don't waste your time messing with your settings, etc. For now, the best course of action is to wait it out.
And to anybody experiencing this problem:
Please don't post "it's working fine for me now" comments as soon as your machine successfully connects to iTunes Match once. If you read the thread, you'll see that we all can connect now and then (maybe 2% of the time?), so please wait until you're connecting successfully consistently over an appreciable length of time before posting that comment. Otherwise, you're inadvertently flooding the thread with (perfectly well-intentioned) false positives that undercut the usefulness of the thread for newcomers.