If you look at a list of new computers, you will notice that a surprisingly large amount of PCs are already shipping with 128 GB or 256 GB SSD. That's gonna hold everything that most people need.
Well, that's a bit difficult to generalize, which is a challenge that computer manufacturer's are having a bit more difficulty addressing. 128GB is fine for a browser/office suite computer, but with the OS taking 20-30GB of that (depending on OS/version/swap file size/hibernation file size), 128GB gets pretty cramped, pretty quickly, if a moderately sized iTunes library is involved. Moreover, phone backups / picture sync for images that are 10MP and higher will eat up that 128GB fairly quickly.
256GB is about the sweet spot for most laptop users, but it's surprisingly frequent that 256GB being enough space is largely contingent upon "data living somewhere else" - be it Teh Cloud (tm), a server share, a NAS of some kind, or an external drive. The ability to stream Netflix and Spotify and at least some iTunes content is definitely helpful, but anemic internal storage is only viable because "data living external to the device itself" has become a way of life for most of those users.