I use one daily, we have several at work. As far as effect on the shot, there is no positive or negative effect. I can't speak for Reg, but I have been told secondhand that the intent behind the ripple was purely aesthetic. The ripple doesn't remain after extraction, anyway.
Though it doesn't seem to affect the shot, the ripple does have a benefit that I have seen... It's kind of like a Circulon nonstick pan - the raised portion takes the brunt of the beating, i.e. when you rest the tamper on your work surface, sparing the low portions from abrasion.
Mmm, juicy. Tastes like juice. Bean juice.