I edited a paper for Journal of Hospital Infection a few years ago on the potential risk of warm air dryers and especially jet air dryers compared with paper towels in spreading microbial contamination via the air. The paper showed that hands dipped in a concentrated bacterial suspension resulted in fairly widespread bacterial contamination of the air; jet air dryers were the worst culprit, followed by warm air dryers, with paper towels resulting in markedly less contamination. They also did some cool paint splatter experiments to visualize potential contamination routes (see image above, from the paper).
Reflections on Infection Prevention and Control 