As I wait (at least another 8 hours, dang it's slow) for the download of the BFD3 Core Library I'm wondering.... where is it downloading it to? 
 
I install on two machines and I'd like to understand how I will do that once the download is done on the first machine.
 
Is it a .zip (or similar compression file)? Will I run an installer? Is it deposited in Program Data?
 
 

It sounds like you're downloading the installer. It contains a sub dir called "payload" which is about 38GB in size. 
 
You have to run the installer. I believe it decompresses/expands/inflates the samples to meet the claim of 50GB. 
 
I installed mine on two PCs (studio rack, laptop) but downloaded it twice. Guess my internet connection is a little more robust, or maybe I'm just closer to the UK. 
 
IIRC, there is an install option to select locations for program (or dll) as well as the samples. My kits and grooves (program data) are all under a custom dir. 
 
FWIW, I like it but had to undergo some user muscle memory therapy. I'm a pretty heavy user and some habits took a hit, but all good in the end. If BFD2 = Sonar 8.5, then BFD3 = X3.  
 

Mine downloaded to the Downloads dir on Win 8.1 (default location).
 

jackson white
Mine downloaded to the Downloads dir on Win 8.1 (default location).
 

 
Mine too. Back that folder up so you never have to download it again. That was painful.
 
Regards,
Dan

Yup, backed up to my Raid-1 NAS. Pretty much SOP for me.