I've been interested to see that Dell is finally selling computers with Ubuntu. We've been looking at new laptops to replace Alisa's computer. (She's currently using my old tibook, which I got in 2001). We went to the stores of both and did a point-by-point comparison of a Despiron and a Macbook. The Despiron is about $250 cheaper -- unless you select the same processor as the Macbook -- then they cost almost exactly the same. And its revolting how Dell puts messages and links everywhere on the Ubuntu pages leading away that say things like "Not sure Open Source is for You? Dell recommends Windows Vista!" As if it was easy to find the Ubuntu pages in the first place -- there aren't any links to them on the front page of the Dell site.
You might think its strange that with a "free" operating system, the computers actually cost more. Rather than adding to the cost of the computer, however, using a commercial operating system reduces the up-front-cost to the consumer by allowing companies to bundle all kinds of trial software, spyware, and nagware on the machines. If you really want a cheap linux laptop, you need to buy the laptop with Windows, wipe it, and then install linux yourself.