They probably have to stage the iso's and everything on the servers. So we can probably pull the final images down before it's announced for a couple hours.
Don't forget to contribute to bittorrent with your iso afterwards.
In fact, don't download over http, just use bittorrent. Leave http for people who don't know how to use bittorrent or otherwise can't (firewall restrictions).
Do you know whether you can use something like bittorrent for the upgrade as well?
This link is a little old and I haven't tried it, but here you go: