You mean Ubuntu lags behind Debian unstable. Debian unstable is constantly
being updated. This is either a good thing or a bad thing depending on your
perspective. I ran Debian unstable for several years and believe me the
quality of Debian packaging varies a lot. Most Debian devs are quite good,
but some are downright sloppy. YMMV. If you want a super stable
distribution, Debian stable is great, but tends to lag a couple of years
behind current development. Ubuntu snapshots Debian unstable twice a year
and cleans up the mess. You can track the development version of Ubuntu if
you want and it will get you closer to Debian unstable, but with possibly
more breakage.
I've not had any problem with GIS on Ubuntu except interfacing with CRAN.
The problem is CRAN is on a rolling update model without any policy about
backward compatibility. (A little like Gentoo, which I also like, but can
be very very messy). I think the R community needs to start thinking about
having stable/unstable branches with a 6 month changeover cycle.
THK