One of the nice things about open source is immediate availability. Let me give you an example... Reading the latest from Debian's release team, it seems pretty clear that Debian Sarge (the next version of Debian, currently the "testing" distribution) won't be officially released until sometime in 2005, if then. Not that the official release date really means anything, since Sarge is already widely in use — perhaps moreso than Debian Woody, the current "stable" release that was officially released in July, 2002.
Because of the way the Debian project has structured their development process, Sarge is available to anyone willing to run the "testing" distribution on their server or desktop. It's also open to any other project or business that wants to utilize the Debian distribution, or its packages.
Several Debian-based distributions, including Ubuntu, Xandros,
Lindows, er Linspire, Progeny Debian, Libranet and the insanely useful Knoppix all utilize Debian's "testing" packages. If you're using one of those distros, you're running Debian.
I've been running Debian testing on one of my servers for several months with no problems. (Current uptime, 103 days. Would be something like 133 days, but for a blown fuse in a power strip...) Thanks to Ubuntu, I'm running Debian testing on a laptop and desktop machine in my home.
So Debian Sarge won't be out, officially, until 2005. Big deal! Debian's "customers," whether that's the individual who installs Debian testing on an aging Alpha workstation, or a company like Progeny that has built a business selling support for customized Debian distributions to other businesses, have access to Sarge right now. From where I'm sitting, that's a much better model than waiting for a grand release of an OS every three or four years.