I use it because it's truly a "complete system" in a way that Linux and even the BSDs are not—every program is an example in itself and it comes with a ton of various scratch-built utilities that you don't usually find as part of a typical Linux distro. Stuff like a basic torrent or IRC client just sort of fall out of the way Plan 9 is organized and implemented.
It also provides me with a distraction-free environment and a set of tools that I enjoy using, even if some aspects of Plan 9 as, say, a laptop daily driver are inconvenient or awkward. It really is better suited for networked computing.
I was pretty much sold from first contact because Plan 9 is the way that I feel best matches what I've always wanted from my machines: a simple grid of networked appliances where I can route the various resources and hardware in whatever way I require.
What happens with the Plan 9 system after the boot camp has ended? From what I can see on that site, their Plan 9 shenanigans will end by mid-September. (SDF is NetBSD-centric AFAIK.)
It used to be that everyone in the Boot Camp got their own VM that was wiped each season, but recently everything was migrated to a single installation that doesn't reset and everyone uses.
In short: now you get a permanent account.
And yes, SDF itself is NetBSD-based—the largest single installation as well as a primary testing environment, if I'm not mistaken.
That's not too hard, given that NetBSD is a niche in a niche. But a permanent Plan 9 server account which I do not have to keep running sounds intriguing... thank you!
Python 2.5.1 was distributed as part of 9front back when it used hg, but it was ultimately removed from the base system once we switched over to git9. 9legacy still packages binaries, however; they're up to 2.7.6 for Python and 2.9.2 for Mercurial.
I never bother with venti/fossil, honestly. I'm more of a cwfs kind of person, but Ori's gefs has been attracting my attention lately.
The "unknown" is Windows. If you change the graph to see the whole range from 2008 to date, you will see that whenever there's a big spike or dip on Unknown, it's the exact opposite for Windows.