Maybe, at some point, we will come up with a use-case that needs more compute that what we currently have, but for most people's current usecase, compute is not the limiting factor.
I could literally eat a 1000X speed increase without blinking.
I think everyone else could too. The difference isn't about speed, but about quality of interaction.
Today's minimal UIs are a good impedance match for the limited cycles available. iOS was particularly good at leading the way on this, creating a UI that was relatively undemanding of raw cycles but still created an unexpectedly immersive experience.
A big part of that was the move from type-and-point to drag-and-tap. The tactile mode, the skeuomorphism, and the portability and instant access compensated for having to squeeze the UI into a tiny screen.
It felt like a more responsive experience even though it was quite a bit slower and more rationed than equivalent interaction on a full-sized desktop.
That's still true today. You can get stuff done on a tablet, but the most efficient and productive UIs pre-ration the affordances. A desktop is much more flexible/general and gives you much more visual bandwidth.
If you apply this idea to hypothetical 1000X hardware, you won't get more of the same but faster - you'll get completely new modes of interaction, which will likely combine the immediacy of touch with the high bandwidth of desktop interaction, and take them much further than anything available today.
It's possible to imagine all kinds of science fiction experiences. The reality will probably still be a surprise.
Even so - the point is really that today's users feel like they're doing everything they want, because UIs are designed without affordances that would be slow and frustrating given today's hardware.
That will change with faster hardware and new designs, and phone UIs will seem as quaint as a 720 x 350 monochrome desktop PC screen running DOS.
Very few hard requirements are valuable today for most users: battery lifetime, hd video for skype/facetime. And maybe SSD, which are now large and cheap enough for people to switch, and get back the bliss of instantaneous reaction again. Other than that no important task will require more than a core 2 duo. They won't saturate Excel (which was not long ago still single core only). In the case they really do, that spreadsheet is probably worth enough to buy a full fledge MBP.
on Windows: http://superuser.com/questions/565347/how-does-windows-limit...
On Linux: https://wiki.archlinux.org/index.php/CPU_frequency_scaling
You can also play with the BIOS, according to https://en.wikipedia.org/wiki/Underclocking
Computing isn't a limiting factor in almost anything we do (I occasionally code and test on a raspberrypi) but we do notice and appreciate the improvements that performance bring. Even naive users notice.