xxcs- An analogy.....
when you say 'things may accelerate'. I agree that incremental growth will hit critical mass and 20% increases will not continue. Based on a crude analogy of a website my sister started a little over two years ago:
We'll just call what she is selling a widget, but a very unique, effective one that is not available anywhere else in the US. She orders them by the box of 100. It took her six months to sell the first 100. But it's the kind of thing that many people must continue to re-order, and a certain percentage would not be without, once exposed. Customer satisfaction is very high. She continued to get glowing testimonials, which she has posted.
Bottom line, she is NOW selling a box of 100 in about two weeks. I see the same thing happening for Wave, and I think there are many parallels with my sister's little website. Weby's famous 'tipping point'. (or Malcolm Gladwell's, but who cares!).