Ubuntu has pushed out Long-Term Support releases every two years that are supported for five years (five years for servers, but previously for desktops it was three years, which has now become five years). Xubuntu, Kubuntu, and Edubuntu are now joining the LTS party with the 12.04 "Precise Pangolin" release.
Xubuntu developers drafted a proposal (email) to make Xubuntu have three-year LTS cycles for i386 and amd64 architectures. The plan for this Xfce-focused Ubuntu derivative is to have "best effort" for high/critical bug-fixes as awell as for security fixes to Xfce-related packages.
The Kubuntu team also drafted a proposal (Wiki), but to make their LTS release be supported for five years (matching that of the new Ubuntu desktop LTS policy). The KDE-loving developers have already followed the Ubuntu LTS cycle, excluding the Ubuntu 8.04 "Hardy Heron" build. The Kubuntu team additionally mentions this 12.04 LTS is at a good time considering Qt 5.0 is imminent and KDE Frameworks 5 is also forthcoming.
Edubuntu, the education-focused Ubuntu, has also drafted an LTS proposal (Wiki). The Edubuntu crew is after their LTS cycle being five years. However, they will be dropping some packages like Mono and thus some programs like GBrainy from their support plan.
During today's Ubuntu Technical Board meeting, the board approved the LTS proposals of Kubuntu, Xubuntu, and Edubuntu. Read the meeting minutes for additional details.