While normally during the current Ubuntu development cycle they are fairly quick with pulling in the latest GNOME development packages since the stable/official GNOME releases tend to happen in March and September just prior to new Ubuntu releases, they won't be so quick to pull in new GNOME packages going forward. This controversial decision came about since tracking unstable GNOME is taking up resources that they could be instead investing in their (Unity) desktop, the Unity desktop is a lot less "stock GNOME" than it once was, GNOME unstable series at times can be unusable, GNOME is not communicating early enough what changes are happening for the next cycle (e.g. the Nautilus file-manager mess in Ubuntu 12.10 / GNOME 3.6), GNOME is shipping stable releases with only partial transitions (e.g. GStreamer 1.0 migration isn't complete for all packages), and the "feedback loop" with GNOME is no longer working well.
The Ubuntu developers say, "our 'feedback loop' with GNOME is not really working nowadays, they don't have time to look at most bugs and we hit regressions and sit on them until somebody on our side has time to look at them, which means neither GNOME or us benefits much from tracking unstable GNOME..."
The problems they see with sticking to stable GNOME releases longer is that there's less opportunity to work with upstream on resolving issues, there would no longer be early feedback on what's happening, and new GNOME library releases might have APIs that Ubuntu application developers want to utilize.
Among the GNOME components thay are interested in updating this cycle include dconf, glib, gobject-introspection, gvfs, and PiTiVi. GTK+ won't be quick to be updated but a daily PPA for the tool-kit is expected. There should also be a GNOME3 PPA for those interested in doing unofficial tests of the GNOME development version.