I just got to thinking the other day (yeah, nasty habit, I know) and I've started to wonder if R5 and Zeta really make a difference any more. BeOS R5, patched or otherwise, is just shy of 10 years old. In the land of Redmond, that's the difference between Windows 98SE and 7. Ouch. Hardware that will run it is increasingly hard-to-find, as well -- unless you run it on a recycled machine, at which point you run into hardware reliability problems at some point.
Although it's only been 2 years since the final release of Zeta, it's also been declared illegal via piracy, so current users are on shaky legal ground at best when using it. It also has a number of compatibility problems with R5 and Haiku, as well. Hardware support has been kind of funny in my experience -- some machines will run it and others not at all. There isn't any binary compatibility with Haiku with anything compiled on Zeta, either, which adds hassle to developers.
Although Haiku has made great strides, it is still buggy, and unless it sees a serious influx of developers in the near future, it will be for quite some time. Should developers even bother with writing code with R5 and/or Zeta in mind? Vote on the poll at the right and let's see who runs what. Maybe that will give a better answer than my own musings. :)