Someone turned me onto Google Trends as a way to gauge the popularity of certain search terms. The coolest thing about it is that you can compare the relative popularity of certain terms. Here are some I found interesting:
The most interesting one was Microsoft vs Linux. The interesting part is that searching for Linux is on a downward trend. The clever among you should be able to figure out why.
I think Google Trends is a good way to gauge market interest in something or the other, especially with respect to related/competitive terms (but not the only way!) I wonder if there are any other ways to do it online.