Most of the Google results I found when digging around on this subject pointed to usual boring causes of slowness: too many programs being run on startup (which you can test with ms-config if you’re running Windows), anti-virus software, and other boring stuff of that sort. In my case, I had been running Ubuntu so most of those tips are moot. But to be thorough, I did remove practically any and every resident program that was running on what should have been a zippy Dell Latitude E6520 with a i7-2720QM (2.20GHz, 6M cache) processor.
And yet, running a utility that averaged about 5 seconds on my desktop consistently took 30 seconds on my laptop. Except for every once in awhile, when it would take 6 or 7 seconds.
Before splurging for a new laptop, I decided to take a peek through my BIOS settings and managed to stumble across the culprit: the Intel “Speed Step” feature. On my Dell, this was under the “Performance” settings. I guess that the idea of Speed Step is that the i7 powers itself down when it decides you’d like your system to perform like a 486. Whatever the logic is that determines when to power down was clearly NOT working as intended on my laptop. After disabling Speed Step, I have been running for the entire day at speeds very similar to my desktop.
Hopefully someone else thinks to Google for this problem and find themselves helped by a similar approach. FWIW I suppose that this might mean that the laptop uses more battery, but you can be an informed consumer about whether you want to run fast or power-efficiently.