Just because an increase in CPU power won't lead to a perceptible improvement in performance, that doesn't mean that your CPU is fast enough. It just means that the bottleneck isn't your CPU at the moment. If all your data were stored on high-end SSDs, and your network connections were multi-gigabit, and your display was 300dpi 120Hz, you would find a faster CPU useful.

Only when programmers are the bottleneck, ie. computers can run the most complex algorithms in realtime, rendering their output at the limits of human sensory capabilities, will we have computers that are "fast enough". Until then, our machines are merely tolerably (or not) slow.

Calling a laptop that still takes more than a second to launch Photoshop "fast enough" is too forgiving - the room for improvement is so obvious that we can only forget it by willfully ignoring and excusing it.

My desktop has already hit this point. Granted I'm not much of a PC gamer or anything, but prior to my current desktop I would upgrade and/or totally replace my main desktop system at least once per year. Now I've got a 4 year old desktop running on a Q6600 and Nvidia GeForce 9-somethingOrOther that I'm still insanely happy with. The only upgrade made to it in the past 4 years was replacing the system drive with an SSD.

Laptops are pretty much "done" for me too if you don't consider size/battery issues -- a Core i5 laptop is more than enough for pretty much everything I do and likely will be for the next 4+ years, but now I just need a smaller, lighter, more battery efficient one.

Then you start running into failure. Modern electronics isn't really built to last, so having a laptop that will last you more than 10 years is extremely unlikely.

Until market demand changes to quality, long-lived electronics, you will still be rolling over your computing device every couple of years. And then there's always the trends and cycles of fashion...