Election Law Blog has a pointer to a paper by two economists,
Does Voting Technology Affect Election Outcomes?", which comes to the conclusion that the adoption of new touchscreen voting technology does indeed affect voting, but the effect was not enough to change the results of the presidential election.
The message that needs to be emphasized is that it potentially could have changed the outcome, especially and easily, in counties with large Hispanic populations in swing states.
Here is the conclusion of the abstract:
We find that the adoption of touch-screen voting has a negative effect on estimated turnout rates, controlling for state effects and a variety of county-level controls. This effect is larger in counties with a higher fraction of Hispanic residents (who tend to favor Democrats) but not in counties with more African Americans (who are overwhelmingly Democrat voters). Models for the adoption of touch-screen voting suggest it was more likely to be used in counties with a higher fraction of Hispanic and Black residents, especially in swing states. Nevertheless, the impact of non-random adoption patterns on vote shares is small.
Note that only the abstract is available at the link above; downloading the whole paper will set you back $5.
I can't do it now, so I'm left wondering how firmly the authors establish their conclusion--that touchscreens changed the outcome, but not enough. I'm also curious about who and what the National Bureau of Economic Research is; they are supposedly nonpartisan, but there are some suggestions (e.g. here: http://www.mediatransparency.org/recipients/nber.htm) that they receive funding from conservative groups.
In the end, the fact that here were some pretty close results, plus some possible vote shaving, doesn't exactly inspire confidence in our system of democracy. And that's dangerous.