I'm not a real roadie but got em and like em (SRAM Rival). Double tap is a really poor description of how the levers work in my opinion. Real description of how double tap works:
1. If you push the lever gently until you feel a click (and resistance increase), then release, you will shift to a smaller sprocket.
2. If you push the lever gently until you feel a click, but carry on pushing further, you will shift to a bigger sprocket. You can change up to three sprockets in this direction if you throw the lever far enough.
I think it works really well. Some people don't get on with it, but the general consensus seems to be that it is a a decent alternative, not really better or worse, just different. Shouldn't take long to adjust.
Also, SRAM Rival as a groupset is a bargain. The 09 version was lighter than Dura Ace, good ergonomics and shifting performance, and similar price to 105.