I cannot really say I am using Plan9 for anything serious, although I have both Plan9 and 9Front running on a couple of old laptops. I keep them around mainly to see if I can grok the ideas and maybe steal some of them :-)
But I run the Plan9port tools on both Linux and Solaris, and occasionally Inferno on Windows, when I want a sane environment there. Acme is my main editor these days. The 'everything is text' approach works very well when developing on multiple paltforms (Solaris, Linux, BSD, Windows). In Acme, the left button combined with the plumber is really usefull when jumping from a debug printout in the log to the source code. I run Vac/Venti on Linux as my backup system both at home and at work.
If I ever get some spare time, I intend to set up a cron job to replicate the contents between the two Venti servers.