Our users may include more tech savvy early adopters than the general population, but capturing that audience is how tech markets are won. This makes our data more relevant as a leading indicator, not less. If you are a major software vendor, and you lose the early adopters, you should be worried.
I voted you up because you made an interesting point here about early adopters, but it would have been nice if you made it in the blog post rather than in the comments here. It would make you more credible. Along a similar vein, you might consider labeling the y-axis on your graphs with something like "% of RescueTime users" instead of "% of computer users." My message is that if you were slightly more qualified in the post, you wouldn't have 75% of the comments telling you that your post is misguided, and instead the overall discussion in the comments here would be much more intelligent.