Ubuntu has always had a Gtk+-policy (well, Firefox and OpenOffice were the exceptions), but today, that has changed. On his blog, Mark Shuttleworth has announced that starting with the release after Natty Narwhal, Ubuntu is going to start evaluating Qt applications for inclusion in Ubuntu's default installation.
According to Shuttleworth, the major issue that needs to be overcome is that Qt applications use a different settings backend than the rest of GNOME. "To address this, Canonical is driving the development of dconf bindings for Qt, so that it is possible to write a Qt app that uses the same settings framework as everything else in Ubuntu," he writes, "We've contracted with Ryan Lortie, who obviously knows dconf very well, and he'll work with some folks at Canonical who have been using Qt for custom development work for customers."
He hopes these dconf bindings will also find their way to KDE applications. "I think it's entirely plausible that dconf, once it has great Qt bindings, be considered by the KDE community [...]," he explains, "Nevertheless, should a KDE app learn to talk dconf in addition to the standard KDE mechanisms, which should be straightforward, it would be a candidate for the Ubuntu default install."
As far as I'm concerned, this is great news. I used to not be a fan of using Qt application in a Gtk+ environment and vice versa, but I think that with enough polishing and backend integration, it should be possible maintain the nice and consistent feel of a strict Gtk+ or a strict Qt environment.