Is meaningful technological growth speeding up or slowing down?  How would we be able to tell?

"Technology is improving faster today than ever" and "Technology isn't improving as fast as it used to" are both plausible statements on the face of it.  I'm not sure how we could tell which is true.  Looking at rates of new patents doesn't seem like a good measurement, since it could reflect changes in how willing people are to seek patents.

I'm starting to find more plausible the dismal hypothesis that technological improvement is slowing down, and that therefore human prosperity around the world is endangered.  Think about the Industrial Revolution.  Think about the automobile, the airplane, the telephone, the lightbulb.  Think about the computer and the Web. Now think about the past ten years.  What's being done that's radically new?  

Of course this is a vague way of thinking about things, and probably colored by my own gloominess.  I'm writing here in the hopes that other people will have sounder methods for looking at this question.

Between 1800 and the present, per capita world GDP increased by about a factor of 16, after centuries of near-stagnation. (Link.)  I don't know why with great confidence, but the conventional-wisdom explanation is usually something like technology, perhaps combined with political or financial factors.  What does seem certain to me is that anything that threatens that 200-year run of good fortune is incredibly dangerous, and we should look out for such risks, unless they're all-but-impossible.  Risks to global economic growth are not quite existential risks, but they're risks to everyone's material well-being.  

Is there anyone here who thinks there exist such risks?