Perhaps there is actually a limit to how much technology there is as Heubner says, and perhaps innovation per capita is declining due to that as people have mentioned.
But I think scientists freely admit there are a lot of open problems,
even in an old science like physics.
To me things like the germ theory of disease, the automobile, electrification, and the radio, out-weigh any of the more modern inventions, in terms of what it means to people.
Since then we had many inventions/innovations, but the big ones that stand out in my mind are: nuclear power, the transistor, and the internet.
Of those, nuclear power's novel effects on society has been largely negative. The non-novel effects are to provide electricity, which is good.
Electronic gadgets (TVs, computers, iPods, cell-phones) becoming cheap and plentiful (made possible by the transistor), have had a pervasive effect, but mainly on our leisure time. They make our schedules more flexible and/or give us more things to do during our leisure.
The computer (one of those electronic gadgets) didn't really have much of an impact till the invention of the internet protocols. IMO, the novel effect the internet had on society was to proliferate the "open" nature of it's design into popular thought. People could already talk to each other over the phone, and broadcast on the radio or print. But these forms of media were controlled by the few. The internet was open to the many (thought still the affluent many) and was extensible. So we get things like the World-Wide-Web, and on top of that social networking, and other things.
Biotech is very powerful, but it's novel effects have yet to pervade society, and people are afraid of letting it happen. We do get better drugs and such, but I would not really point to it as life-transforming for the many.
Nano-tech is in its infancy, we'll see what effects it will have.
So my theory is that people have more than a little comfortable. There is just not as much need/demand these days for technology (at least on the surface). Necessity is after all the mother of invention.
The great needs of today, have to do with resource conservation. Getting a fairly clean, renewable (and/or abundant) energy source is our biggest technological hurdle.
Perhaps damage control or reversal is another one.
But these things are really only affect society by the absence of affect. That is, we know our lifestyle is not sustainable, but we may yet find ways to make it so.