With its scheduled April 24 release of Ubuntu 8.04, which also goes by the alliterative moniker "Hardy Heron," Canonical will ship its second "long term support" (LTS) version. But the first, really, since the company and distribution became widely popular.
There's always been a bit of a flavor-of-the-month aspect to Linux distributions other than the big two: Red Hat (along with its Fedora community version) and Novell's SUSE. Gentoo grabbed headlines one year; Mandrake was supposed to make the Linux desktop a widespread reality another year. It might be tempting to paint Ubuntu's current popularity in a similar light but I think that would be unfair. Ubuntu is really a more consumable flavor of Debian--which has long been a popular non-commercial alternative to Red Hat and Novell but has equally long held a reputation for being geeky (as in hard to install and configure) and for having a often prickly community.
The relationship between Ubuntu and Debian is more fully described here, but in a nutshell, Ubuntu is built on top of a Debian foundation but has its own community and release process. Ubuntu is also supported by a company, Canonical, whereas Debian is an (aggressively) volunteer effort.
Hardy Heron comes in two builds, one with packages oriented around server use (Ubuntu 8.04 LTS Server Edition) and another around desktop applications (Ubuntu 8.04 LTS Desktop Edition). The two different builds also have different support windows during which Canonical commits to release security fixes and other updates. For the server it's five years; it's three for the desktop. Gerry Carr, Canonical's marketing manager, told me that's it's also possible that the server edition could also end up shifting to a longer cycle between releases than the desktop version--although no decision on this has yet been made. The idea is that the balance between stability and having the latest and greatest tends to tilt harder towards stability in the server world than on the desktop.
Gerry also said that Canonical has started putting more focus on the server edition and its associated community than it has over the past couple of years. Today, Ubuntu is generally perceived as an easy-to-install desktop Linux distribution. Outside of some specific areas, such as its (unsupported) port for Sun UltraSPARC hardware, Ubuntu isn't viewed so much as a server distro. Canonical wants to change that.
Ubuntu's release schedule is currently configured to have an LTS release about every two years with non-LTS releases (which have 3 year and 18 month support windows for server and desktop respectively) filling in the gap about every six months. Thus, in 2006, we saw the release of Ubuntu 6.06 LTS followed by Ubuntu 6.10, Ubuntu 7.04, and Ubuntu 7.10. The interval between LTS releases is similar to that for Red Hat's and Novell's Enterprise releases. The difference with Canonical's scheme is that there is no separate stream of community releases. Rather, certain releases are designated LTS to give hardware and software manufacturers longer cycles for their certification process. Both LTS and non-LTS releases can be downloaded and distributed at no charge with the option for a support subscription also available in both cases.
Canonical says that they have relationships with more than 30 PC manufacturers (many of them regional) as well as dozens of commercial ISVs, Open Source and otherwise (IBM Lotus Notes, Parallels, VMware, Alfresco, Zimbra, etc.). The nature of the relationships vary. Essentially, support in this context means that Canonical guarantees that the package will install smoothly on their distribution. However, whether a given application is supported, by Ubuntu or the ISV, in the sense of "I want someone to fix my application because it's crashing" will depend on the specific commercial relationship. Thus, not all supported applications are necessarily "certified" in the sense that term is typically used in support contracts for commercial operating systems and applications.
However, at this point in time, I don't see a lot of call for another Linux distribution in the Red Hat Enterprise Linux or Novell SUSE Linux Enterprise vein anyway. These companies put a lot of effort and resources into getting lots of applications fully-certified for their platforms. At Brainshare last March, Novell's Linux marketing director Justin Steinman told me that getting even more apps certified, and thereby close the gap with Red Hat, was one of his highest priorities. And you pay for that effort and the peace-of-mind it brings when you purchase a support contract. Canonical's offer is softer and cheaper--more pitched to those who have been running Debian either unsupported or through a third-party support contract with the likes of HP.