Okay, don't get your hopes up, but iTunes Match has worked, so far, for me in the last 2 hours or so. That doesn't mean the problem is fixed. But the reason I'm posting is that something got me further than before.
If since August 7th you have not got past the message "Sending information to Apple" .. listen up. The same thing kept happening to me, happened every time except for once, and then I would go on to get the error message.
But just now I read back through this thread to the instructions for clearing the cache (on Page 5 of this thread - I don't know how to link to the specific post). Anyways, I tried that, following the instructions very carefully and I was able to complete the iTunes Match process.
However, what you have to do for this temporary workaround is to clear the cache before each attempt to update iTunes Match. And it doesn't take that long to do so, once you get the hang of it.
Also, please note that I think resetting Safari if you are on a Mac will accmoplish the same thing as the instructions for clearing the cache. DO NOTE that resetting Safari may mess up your Play Counts if you have not already synced with iTunes Match lately, so I wouldn't recommend doing this if Play Counts are important to you.
I'm not saying this is a solution by any means, because it has only been working for me in the last 2 hours. But, before I couldn't even get past the "Sending information to Apple" message, so I'm much more optimistic than I have been since this problem arose for me.
So all I'm really saying is this: If you haven't cleared the cache, I don't think there will be any way for you to update iTunes Match until this problem is resolved. Clearing the cache doesn't solve the problem - the servers of the service itself still have to be up and running. But what I'm thinking is that unless you clear the cache, there will be no way for you to connect to the servers when they do come online in your area, which people are reporting happens intermittently.
Hope that makes sense and hope it wasn't too repetitive. Good luck. I hope they resolve this soon.