Help! My patch isn't downloading? It's stuck at 68%/73%/xx%!
It probably is downloading -- be patient and let it run. Blizzard uses a Bittorrent-based system to distribute the game's patches through the official client, and those systems depend not just on Blizzard and their ability to distribute the patch, but also how much of the patch all of your peers have. If everyone around you has xx%, that's all you'll get for now. But an hour from now, someone will have spread the full patch around, and then you'll pick it up no problem. Patience is a virtue, and until the realms come back up, you can't play anyway.
Also, the patcher will stop showing progress around 70% or so -- at that point it'll start installing the patch, and you'll need to click another button to see installation progress. But if you just let it run, it'll update.
What does "The tracker is not responding" mean?
Another Bittorrent issue that should resolve itself after a little while. The patch will need some time to disseminate, and if you get a message like this, it just means your client hasn't found all of the connections that it can. It will.
I get a weird "Unable to Validate Game Version" message when I log in. Is my client broken?
No. Blizzard's servers aren't all upgraded yet (hence the reason we can't play). When they are all upgraded, your client's version will match the server's, and everything will be hunky dory.