Let's see... Off the top of my head: Debian, Ubuntu, yiffOS, Arch, Gentoo, Red Hat, OpenSUSE, Mint, Fedora, Tiny Linux, Mandriva, CrunchBang, Raspbian.
i had some good times squeezing every last package down to the bare minimum and watching my RAM and CPU utilization approach 0% via the resource monitor widget for tint2
only to have the laptop crash from tying to get a little too creative with fractals in Synfig :]
I don't even remember how I heard about it. I think maybe I had a live CD that I messed with when I was a teenager, but I can't remember. I know I had live CDs for Arch and Mandriva though.