It's pretty easy to keep up to date with 2.6.x.y on Debian.
sudo apt-get install ketchup make-kpkg
Keep an unpacked copy of a recent version in your home directory, then:
cd linux-*
ketchup -r
make oldconfig
make-kpkg --rootcmd fakeroot clean
make-kpkg --rootcmd fakeroot kernel_image
cd ..
and sudo dpkg -i to install the new kernel package.
Haven't tried this on Ubuntu.