Recently there's been some discussion about the possibility of Ubuntu switching to a rolling-release distribution. That's not a good idea, and this is coming from someone who loves rolling-release distros.
Consider Ubuntu's old slogan1: “Linux for Human Beings”. For Human Beings. That means their main goal is (or, was, see footnote one) to make a distribution for your “average-everyday person”. Ubuntu, as is, with it's 2-year LTS and 6-month regular releases, is pretty well off.
If you look at the two big competitors to Ubuntu, Windows and OS X, they don't have a rolling-release style of updates because that means users have to spend more time updating their system over time, as opposed to spending maybe an hour (or letting it run over night) on upgrading to a new version of the OS.
For the target market of your average person (specifically, not one of them computer geeks), the LTS is the way to go. They install their shiny, new operating system, use it for two years (or, up to five, if they so desire), then upgrade to the latest LTS, and repeat the cycle. It's almost exactly the same as Windows and OS X, just on a strict, every two years release cycle.
While I no longer suggest Ubuntu proper to people looking for a linux distro to try out (Xubuntu/Kubuntu/Ubuntu Gnome Remix are still on the table, depending on what someone needs), or attempting to breath new life into an older computer, or any number of other things that Linux is useful for (read, everything…), most of the suggestions I give to new linux users and non-linux nerds are based on Ubuntu. Switching to a rolling release screws them over. While most could probably adapt, a rolling release isn't all that friendly to ye-standarde-personages.
Ubuntu still holds a special place in my heart because it was the first Linux distribution I ever used, and, like I mentioned before, it's the basis for a good majority of distros I like for various reasons. It's no longer a part of my daily life (I've since switched to Arch Linux, which is a rolling release distro, but that's because I think I can fairly competently figure my way out of any mess that I might cause), but for a large majority of newer linux users, it was their gateway into the world of Linux.
Being easy to use and stable is Ubuntu's greatest advantage, why throw that away by introducing the possibility for everything to get changed at once? And what of those users who use something, and like the way it works, should they have to learn how to keep it at its current version and keep it from updating when they see new updates? I wouldn't think so.
Update (31 January 2013): I've received a couple comments along the lines of not being explicit on why this would be a bad idea. While I feel there's an adequate why that can be inferred, here are some more thoughts, and a couple anecdotes.
The why is that rolling releases lead to more changes, faster, which are bad for the two big focuses that Ubuntu has: standard computer users and businesses.
Consider Google, who uses a slight derivative of Ubuntu (mostly getting rid of any software that phones home and battening down the hatches) uses the LTS as their basis, because it's extra stable.
Canonical even advertises that LTS releases are supported for a fairly large amount of time. You could argue that the support of a specific version goes away when there aren't versions. But, by having versions, they've explicitly stated that software, and more importantly to the end-user, their desktop environment, isn't going to change except for bug fixes until they install the next version.
Shiny, new versions of software is nice, and for people who want it, it's nice to be able to install it, but it removes the stability for the two targets (the aforementioned standard computer user and businesses).
If you the head of an IT department for a bank (and for all I know, you could be), would you choose to use a rolling release distro that could potentially release a big change to software used and require lots of effort to either switch back to the old version, or teach everyone how to use the new version, or would you choose a stable release distro? Keep in mind that rolling releases don't release all of the new versions of software at once, which means you have to make that choice for every piece of software that changes, and at different times.
For the most part, you wouldn't. You would go with stable.
Consider someone coming from the “wonderful” world of Windows. Lets say they install their operating system right before Gnome 2 is switched to Gnome 3. They have a nice setup, they like how it works, they've figured it out. One day, they run their system updated, suddenly they've got Gnome-Shell, and don't know how to get to fallback. Think they want that? No, they want stability. They want to know that there won't be any big changes until they decide to upgrade to a new version of the OS, probably in two years.
It seems that Ubuntu no longer uses the slogan “Linux for Human Beings”, which is a shame, because it was a great slogan, and it captured what Ubuntu was at the time.
I think the dropping of the slogan is a little symbolic of the current state of Ubuntu, no longer specifically for human beings, but more for doing what Canonical wants, the way Canonical wants it. I don't have a problem with that, Canonical is the benefactor and main development force for Ubuntu, and it's their baby, I just don't share their vision of the future (or specter of the past).