I'm happy withe SRAM Rival components on my current bike, but I was also happy enough with the 105 components on my previous bike. And after the crap Tiagra derailleur broke, I had an Ultegra which never gave me any trouble.

I got the new bike because I needed a frame that fit me better. I expected to get a 2011 Madone 4.5 with Shimano components, but the LBS happened to have a 4.7 from 2010 on sale for the same price, and it came with SRAM Rival. If the 2010 bike had not been available I expect I would have been happy with the 4.5 and its components.