Well, ubuntu's not for sale -- I'm sure someone will charge you for it if you want, but you can't walk into a store and buy it. But you can get some netbooks, laptops and desktops preinstalled with it, and their publicity and userbase evangelism has certainly increased their marketshare; even 3 or 4 years ago, you'd have been hard pressed to find a linux distro that had the kind of community and popularity that ubuntu has now. Redhat might have been close, but their focus on corporate money/marketshare put a bit of distance between the average user and them; debian has the fanatical userbase, but can be technically difficult for newbies and is therefore destined to never have the broad userbase that ubuntu has. If you're looking for a desktop OSS OS, it's not only available, you can get it preinstalled already. And they've got help/support etc forums available.
Be's downfall was threefold: no apps, no inroads to consumers and Apple went with Jobs' NeXT instead of Gassee's BeOS. Haiku's OSS nature means it can't be killed in the market -- there's no market that it *needs* to survive -- but without some kind of push to get it going and into people's hands, it's going to be as great as the next linux distribution you've never heard of. Which is a shame, because it's a nice OS.