About a year ago i bought a Macbook Pro and made the change to Mac OS X from Windows, and for a while i became a true Mac-Zealot. Then as now i was enthusiastic about open source software and hell i discovered a lot of small and nifty applications for OS X. However more often than not i found that the best Open Source applications was made natively for Linux and then ported to Mac, and the best games were made natively for windows and often not ported at all. At first i was perplexed that software manufacturers did not develop for Mac. But as i became increasingly aware of Apples company structure, it wasn't startling. In How Apple Got Everything Right By Doing Everything Wrong Wired describes the Apple company as the Evil Genius in vivid detail. I won't go into further detail on the article but i truly recommend you read it, especially if you are a dedicated Apple fan the article can put things in perspective.
Motivated by moral reasons i finally installed Ubuntu on my Macbook Pro. The change did not involve major complications. In fact the synaptic package manager puts more order into your computer than any drag and drop interface and gives you access to an ocean of amazing Open Source utilities making ubuntu a good choice for both the casual and the professional user. Unless you are a hardcore gamer ubuntu will most likely more than suit your needs.