If you're trying to run AA3 after the preload or after you've downloaded it and it tells you "steam servers are not available, try again later" there is a fix.

This might not work for you, but it does work for the majority of the people who try it. It doesn't work for about 1 in every 4 people, so you've got a pretty good chance of it working.

1. Go to: http://store.steampowered.com/stats/content/
2. Click "View individual server statistics"
3. Find an unfiltered server that has low usage and select that country by going to Settings and Downloads (in the steam client). Indonesia worked fast and flawlessly for me, and I'm in the US with a speed of 150kb/s. It should work for you too.
4. Restart Steam and your files will decrypt.