Its web browsers - with Mothra probably being the least bad one - are fine if you don't rely on webshit for your daily work. As the Harvey project is mostly stalled and Jehanne lacks manpower, the first steps into efforts to port NetSurf to Plan 9's APE(X) library have not come far yet.

With this elephant out of the room, I think it depends on what you want to achieve. Plan 9 is a sufficient operating system for Go (and, at least, because of the special syntaxes, some C and shell) programming and its Fossil/Venti file system combination makes it a fine backup station, especially when clustered with other Plan 9 machines. Nevertheless, I don't think that anyone who runs an actual desktop system, even if it's KolibriOS or RISC OS, would have an advantage from completely moving over to Plan 9.

It has its niche and it fills that niche well.