About 6 months ago, I've seen a usability study of a downloadable app (P2P/Bittorrent app to download movies, music) and they tested in on 5 people. Users had to download the app, install it and then use the site to start the downloads. Out of 5 people, not a single person managed to complete the task because everyone was suspicious of installing anything.
The aversion to install anything and fear of viruses and spyware is absolutely amazing.
We have a much larger sample at RescueTime.com and we're seeing this... But it's not too painful. Our conversion rates are pretty outstanding (20% or so of absolute uniques download our software).
It's all about credibility (a bit harder to establish with no-name p2p app).
The aversion to install anything and fear of viruses and spyware is absolutely amazing.