Interesting question, since the HDD makers keep producing bigger HDDs, and probably beyond the capacity for many to use that much space.
Let me take an inventory . . . I've fitted most of our machines with StarTech hot-swap SATA bays and caddies . . . . I count seven caddies with HDDs ranging in size from 500GB to 1TB. And they don't get a lot of use, since our WHS-2011 server seems to take care of client-workstation backups with great reliability.
There are ways to make HDDs more quiet. There are ways to cache an HDD or array to an SSD or to RAM or both -- even (and no less) on a server.
So while I agree with corkyg about our laptops, I think that I will still provision an HDD for use in my Z170 system when I get around to building it.
How many folks have HTPCs? And how many of those simply allow a gaming system to do double-duty as an HTPC? If you record a lot of TV shows and movies, are you going to put "the data" on an SSD? I think not. You wouldn't even bother to use a caching solution to speed up an HDD used for that purpose.