I used to tell people that Slackware was a great distribution for learning how everything is put together, b/c you had to configure everything to get it to work. These days, a lot more of it works out of the box. That said, if you want anything that's not in the mainline distro, you get to learn about slackbuilds.org or compile it yourself (makepkg is your friend).
If I remember correctly, Backtrack is based on Slax, a liveCD distro based on Slackware. So it would probably be a good idea to learn it anyway.
I don't mean to scare you off of Slackware. I learned *nix on that and FreeBSD back in the mid 1990s, and I still run Slackware today. But my wife's netbook runs Kubuntu.