And that includes today, folks. Get it here, if you want it. On that same page it says, "...available until August 20th". I believe that means *through* the 20th, not to the 20th. You should be able to continue downloading until the end of day on the 20th, though I don't know what time zone will be used to mark the end of the day.
Also, keep in mind that it will take a while to download, possibly a few hours, even on a broadband connection. The x86 DVD image is 2.35 GB, and the x64 DVD image is 3.04 GB. As others rush to meet this deadline, the servers hosting these files may slow down even more so keep that in mind as well.
Even though the Windows 7 RC downloads will be unavailable from MS after August 20, you will still be able to get a license key to install it with. Here are the important dates:
8/20/09 - Last day that Windows 7 RC will be available for download
10/22/09 - Windows 7 ships (General Availability or "GA")
3/01/10 - Windows 7 RC will begin shutting down every 2 hours
6/01/10 - Windows 7 RC expires & RC license keys no longer available