Users aren't installing Torbutton
We have two studies now that indicate 18% or less of our users are actually using Torbutton. One study measured the frequency of Torbutton user agents in HTTP requests and found that only 18% were Torbutton. Another study found that something like 50% of Tor users were logged in to their gmail accounts, as compared to 45% of the normal population. The methodology of both studies weren't great, but regardless of this, it's clear that the installation base of Torbutton is significantly lower than we would like it to be.
In our Mac OS bundles, its easy to see why most users are not installing the addon. The installation script is a weird looking thingy at the bottom of the window next to the License and ChangeLog files in the dmg. These files should not be cluttering that window, and the Torbutton install script should be more strongly labled as "CLICK ME!" if it cannot be autolaunched.
More long term, we should investigate having Vidalia install Torbutton, and/or some form of user agent header check by Tor itself. In the meantime, our bundles should all be tested for usability and functionality in terms of the Torbutton installation.
If Torbutton does not get installed, there is no point in most users even installing Tor.