For many years I never considered anything other than a 7200rpm hard drive for my laptops. With my most recent laptop purchase, however, I elected to go with a 5400rpm drive for the first time. The main reason: heat! After doing a ton of reading about performance, nobody doubts that a 7200rpm drive is faster than a 5400rpm laptop hard drive. In my opinion, however, the small performance advantage one gets from a 7200rpm drive does NOT outweigh the significant increase in heat generation that comes from selecting a 7200rpm drive over a 5400rpm drive.
Along with the extra heat generation comes an increase in power (and therefore battery) consumption. Because I use my laptop often on the train, I like to maximize my battery life, and having a 5400rpm drive is one way to do that.
As portable computers get smaller and smaller, heat generation becomes more and more of an issue as more heat-generating components are packed into an ever shrinking space. So the next time you purchase a laptop, consider the size of the machine when it comes to heat generation, and also think about battery life as the faster 7200rpm drive will drain your battery more quickly than a comparably sized 5400rpm drive.