Until now, people who downloaded non-LTS (long-term support) versions of Ubuntu were treated to a lengthy support period -- a full 18 months. Now, though, Ubuntu's technical board is shortening that support window to nine months, in the hopes that Canonical can assign its engineers to other projects. (If you look at the board's meeting notes at the link below, the group also agrees that most bugs get fixed within nine months anyway.) If you're wondering how this might affect you, the new policy applies to version 13.04, along with all future non-LTS releases.
Separately, the board decided that it will switch to a rolling release model, in which users won't have to do a full system upgrade to take advantage of major OS updates. Many of the particulars there are still up in the air, though, which is a shame because this has already been a hot topic of conversation in the Ubuntu community, and quite a few folks are likely to be curious. In any case, for those of you who want to know more, we recommend checking out those meeting notes to soak up as much detail as you can.