I'm an Ubuntu linux user, as it's widely supported, easy to install, and a breeze to update software using Synaptic. I do admire other distros (I've a soft spot for the vehemently Free multi-media dynebolic, the audio-rich pure:dyne (made by goto10), the minimalist ubuntu-based #CrunchBang) and since acquiring the snazzy Acer Aspire One netbook, I'm always on the look out for lean and mean linuxes.
Roll up Puppy Linux. Yet Another Linux Distro!?! No, it's not just another distro, this one is different and this is why. It runs off a live CD but the coolest thing is that you can now make your own custom cut-down Puppified linux from the distro of your choice using Puppy Woof!. Woof (made by the Puppy originator Barry Kauler) will automagically download and strip out the fluff, bloat and bumph from a variety of different distros (currently Debian, Ubuntu, Slackware and Arch).
A couple of provisos. I haven't actually used it yet, I'll leave that to my friend oiio who passed on the link. And it's designed for developers, not end-users. But still, I like the idea of a Fluff-Free Lean'n'Mean Linux Machine ©.