The more I read and think about this, the more there is to read and think about. What's very cool is that I can go to the Bike Archive on Trek's website and get the specs for the road bike that I bought in 2003 and replaced with my current bike in 2010:

Shimano 105 52/42/30
Shimano HG-50 12-25, 9spd

So I can run those numbers through Sheldon Brown's gain ratio calculator for comparison to what I have now. The old bike had a triple, and I mostly used the middle chain ring, though I never hesitated to drop to the granny when I felt it was necessary. Before buying the new bike I made sure that the lowest gears were comparable to the old one, but now I will look more closely at how the middle ring gain ratios compare to the gears I often use now with the compact double.

In another thread we recently talked about the aging brain, and how it's harder to learn new things as we get older, except some things that really interest us seem not so hard to grasp. This is a perfect example for me -- learning more about gearing is interesting, and therefore relatively easy.