Ever since windows update blew up windows a few years back, I desided it was time for something else. I had messed with Slackware years before, but the desktop was still pretty young back then. My Dad started using Ubuntu around version 7.04, and I liked the look of it.
Since then I have played with many linux distributions, mostly live cds (great way to test drive a distro). Certain distros are aimed at certain uses. System Rescue CD, Ultimate Boot CD, and Parted Magic are very good 'tool box' live cds. They are not even made to be installed, but are invaluble for recovering files, wiping a drive, and repairing windows (Take that Bill Gates). Two of them have enough to get you on the internet to download drivers to get a windows box running.
Puppy Linux, CrunchBang Linux are both good distros for older computers, as they are made to be light duty but very fuctional. CrunchBang is on my laptop, on which I am typing this right now.
Ubuntu is a good stepping stone for those that are use to windows, but once you get more comfortable, there are better. Ubuntu keeps getting more and more bloated with their desktop version, and they don't seem to care about community oppinions anymore. Debian is the parent of Ubuntu, and makes great efforts to make a stable clean distro.
Links of interest...
Big 3 linux distros
50 places linux is running