I got curious today, and ran vrms to check which non-free packages I had.
To my great surprise, no kernel packages appeared.
It used to be the case that the kernel contained some small non-free bits (like firmware) that made the package unfree.
I am wondering, now, if vrms is lying, or if all the non-free bits are out of the package?
No, ubuntu kernel is not 100% free, It includes some non free kernel blobs.
source: http://www.gnu.org/distros/common-distros.html (just look for ubuntu)
There is an another distro called gNewsense which is based on ubuntu but removed all traces of non free components. For a list of 100% free distributions, look at http://www.gnu.org/distros/free-distros.html
For the record, just what constitutes "free software" is to some degree up to interpretation. The FSF has the strictest guidelines for what counts as free software, but Debian is slightly looser than the FSF on what it will accept. vrms is based on the Debian Free Software Guidelines, and accordingly some packages that the Debian developers are ok with won't show up when you run it. vrms is not "lying", it's giving you its interpretation of what non-free packages you have installed.
Although I'm personally of the opinion that it's a very useful tool, the FSF doesn't endorse vrms because although it uses RMS' name, it doesn't follow his guidelines. Not only does it miss some software they consider non-free, but it also at times flags packages (mostly documentation) written by the GNU project itself.