The Daily WTF has a funny story around intentional slowdowns. I have one story to share as well.
Back in the college days, when we were still busy with exams and courses, some of my friends started working at various companies in our city (Bucharest).
One of them managed to get a contractor position at a certain software company. His job was to take a certain application developed by that team (let's call it "Standard"), and to create an "Advanced" version of that application, since some customers were willing to pay to upgrade to a more powerful version of the same app.
After a while, the "Advanced" version of this application was presented to customers and they were delighted. Indeed the application seemed to be more powerful than its "Standard" counterpart - it certainly spent more time "thinking" when it performed certain tasks.
What was the secret behind the Advanced application? After a couple of beers, my friend told me: a bunch of inserted Sleep() calls.
P.S. I haven't heard from my friend in a while - his contact with the software development industry was very brief.