My wife has an iBook I bought her, because I didn't want to go through all the hassle of ACPI with Linux (sleep, hibernate problems), WLAN drivers, etc. (and no Windows box, needless to say, enters our house).
That machine is stable and works very well.
Nevertheless, I prefer using my Fedora 5/6/7 and CentOS 5 boxes (a test pc and a stable one). It is consistent, stable, free as in speech (free as in beer is not an issue, I pay for my Linux too), lots of software is available, I understand Linux, I feel at home with it, and less of the 'Unix layer' is hidden from the user than is the case in Mac OS X.
About the command line and some people fearing it: I use the CLI on OS X too, because I don't always like the Finder and I use some programs I like, such as MPlayer, on OS X on the CLI. Without the Darwin ports I couldn't find OS X usable.
For those that want a Fedora just to be productive and not to mess around with, with the minimum amount of bugs, and which has a life span of five years, I recommend using CentOS 5, which is actually Red Hat Enterprise Linux 5, rebranded from the RH source.
A Mac User's Opinion of Fedora Core 6