Is anybody installing?
For some reason the installer is downloading another 8 gigs. (Which makes sense since the pre-install was only ~7gb and the website says that a minimum of 15 gb is necessary).
by the way, if you downloaded the installer from battle.net, installed the initial 7 gbs, and then deleted the installer, then tried to run the Diablo III Setup.exe, it won't work (You will get unexpected decryption error). You'll have to redownloaded the 30mb installer thing from battle.net which will finish out the install.