One of the reasons that I bought a MacBook was the prospect of running any OS that was likely to come up in my work could be run on the laptop. At the time, I assumed that I'd use Parallels for this purpose and in fact bought a copy of Parallels the same night that I bought the Mac. I've been using Parallels since then and while it has worked, the experience, especially with Ubuntu Linux 7.04 was less than seamless. Installing was a fussy process and I could never get the display working to my satisfaction in full screen mode. Also, I was unable to dedicate more than 512M of memory to the Ubuntu instance.
Then, I gave the VMWare Fusion beta a try. This was the seamless operation I was looking for. The install went without a hitch, after installing the VMWare tools the Ubuntu display automatically adjusted to the size of the MacBook display in full screen mode. It's also quite responsive, I can dedicate a decent amount of memory to the instance and copy and paste works. This is very cool. I took advantage of the low price ($39.00) during the beta period and chalked up the $79 I paid for Parallels to experience.