I've been exploring gearing options, and came across this nifty gear selection tool, at Gear-Calculator.com.
Here I compare the 53-39 double with SRAM 11-36 10-speed cassette, as seen and discussed on this Paketa, with my setup, which is a 53-42-30 triple with Campy 12-29 11-speed.
This nicely visualizes and quantifies what you get with each setup. The 2X 11-36 has quite similar range, but not nearly the close spacing of the 3X 12-29.
I really appreciate this close spacing on the riding we do, for example, keeping up with fast single riders on rolling terrain on our club training ride. Making many small shifts while keeping optimum cadence allows us to mix in with the half-bikes, which in comparison to tandems have more variation in speed and rapid accelerations.
[The graphic was posted by doing a screen shot by pressing CTRL-PRINT SCREEN while on the site, and then PASTE in MS Paint, a Windows accessory program. The image is saved, and then uploaded to Flickr, or easier yet, Tiny Pic, which will provide the IMG code to past right into the post.]