The Secret Lives of Ubuntu and Debian Users is an article which looks at the package install and use date from the popularity-contest package. There are some interesting conclusions that can be drawn from this data:
The Ubuntu results list 425,490 installations of Firefox 3.0, only 92,629 Votes and 63,034 Recent upgrades. In other words, although roughly half of Ubuntu installations reporting include Firefox, only about 20% have used it in the last 30 days, and only 13% have upgraded it.
With IceWeasel, Debian’s non-branded version of Firefox, of 46,276 installs, only 25,797 46% are recently used, and 11,207 24% recently upgraded.
Percentages differ for other packages, but in almost every case, figures for use and upgrading are much lower than for installations. Probably this difference reflects how easy GNU/Linux distributions make the installation of software.
However, what is less obvious is why, when automatic upgrades are available on modern desktops, most people are not upgrading as soon as new packages are detected — or perhaps not at all. Apparently, the average Ubuntu user and, to a lesser extent, the average Debian user, are far more cautious about upgrades than you would expect from their availability.
Another way you can use the popularity-contest data is as a measure of how comparable software is being used. For example, both Ubuntu and Debian show high numbers of GNOME desktop installations, as you might expect from such GNOME-centered distributions: GNOME is installed on 85% of Ubuntu installations and 50% of Debian installations, and has been used recently by 78% of Ubuntu users and 55% of Debian users.
The relatively low number of Debian users is probably explained by the fact that the distribution appeals to more advanced users than Ubuntu, and such users are more likely to choose one of the dozens of alternative desktops or window managers available, or even to use the command line.
The article is well-worth a read and gives some insight into possible differences between Debian and Ubuntu users, though none are particularly surprising.