I'm somewhat embarrassed to confess that I upgrade my primary laptop pretty much every year, whenever Apple comes out with an updated MacBook Pro. My work is very computationally-intensive ("big data" stuff), so having the latest-and-greatest has an actual impact on my productivity.

Thankfully, Apple products tend to hold resale value so well that I can usually do this for about $500 out of pocket after selling last year's model on eBay or Craigslist. The way I look at it is that I'm "renting" a high-end laptop with full warranty coverage for a bit more than a netbook costs.