There are close to 400 Linux distributions out there according to Distrowatch, so a new distribution getting traction is hard. SuSE, Fedora, Debian, etc. have a strong following.
There are various numbers being thrown out about which Linux distribution is popular, which one is gaining traction, etc. Most of these numbers haven't been arrived at scientifically.
So, I thought about using one of the most reliable methods/tools: Google. Search for the words Linux followed by the name of the distribution and see how many results Google comes up with. Some Google hackers and marketing folks call this market share info. I would classify this as Web presence.
Here are some findings: Ubuntu has twice the Web presence of Knoppix and much more than Mandriva. Red Hat is the leader, followed by SuSE and Debian.
I plan to do these searches every couple of weeks, to find out trends on the Web, news and blogs.