After having used Ubuntu for a week (current uptime: 7 days, 9 hours), I understand why it is the most "popular" distribution on Distrowatch in recent months. The focus is on the user and on the home desktop, unlike larger distributions like RedHat which focus on enterprise servers and desktops. Debian's apt/synaptic combo is nicely packaged into an update manager that notifies you, much like up2date in RedHat.

On the other hand, I do not see much difference from Fedora. Most of the desktop related improvements are flowing upstream into Gnome, and some improvements such as Fedora's NetworkManager are missing. Fedora is better supported for Java development by jpackage; I can find no such Java package repository for Ubuntu. Multimedia and "non-free" packages are not included in either distribution (Gentoo beats both in sheer package coverage).Finally, I am heartened by the fact that much the same people who work on the enterprise-class RHEL also work on Fedora, and bring at least some of the associated QA mentality to their Fedora work.

For instance, since the release of Hoary, there has not been a single kernel update on Ubuntu. My experience on Fedora was quite different; my low uptimes were invariably due to new kernels with security fixes. Perhaps the current hiatus is due to Linus' SCM issues; otherwise, despite shipping a very recent (relatively unstable and untested from a security standpoint) kernel, Ubuntu is not keeping it up to date.