For many users, computers are already "fast enough".
Search for tales of folks using old computer for servers, web browsing, word processing, etc. MS Office, for example, hit Feature Saturation for such a vast majority of users a LONG time ago, so "old" software, on "old" computers is more than adequate to fulfill the bulk of most normal folks tasks.
The two current "big" CPU syncs (for most) is basically the Web Browser and Flash, or video games.
Before Web browsers primary task was formatting layout. Now, they're more and more becoming Javascript runtime engines, that happen to render HTML, which can be really CPU intensive.
However, most 2-3 year old machines, especially with modern software, run even heavy JS browser apps quite well.
Notice that we have not seen a large bump recently in actual CPU speeds. Rather we are focused now on cores, power management and heat. This is another sign that the computer is "fast enough".
Now, certainly there will always be tasks that the computer isn't fast enough for. 3D rendering, movie rendering, vast scientific models, etc.
Plus with our ever larger appetite for creating and collecting more and more and more data has some impact on performance. But even that's more and more specialized in business and industry rather than at the consumer level. And at the consumer level it's more a storage issue than a processing issue (save for actual movement of data, say for copying).
A DVD ripped to a hard drive is large, but, today, not particularly taxing for modern systems.
Todays primary complaints about speed are I/O bandwidth mostly, and recently there was a blurb that of the folks in the US that don't have broadband high speed net connections, 1/3rd don't even want it. They don't see the value proposition of it.
So, for some cases, the answer is "no", computers will never be too fast. But for many, even today, computers are "fast enough".