In a word, dismal. They recommend you VNC over to another machine for using a full web browser, since the current existing browsers are far from modern (think Mosaic-grade with some CSS support)

Sad to hear. You - by any chance - don't have any dev experience for plan 9 apps itself do you? Would be interesting to find out how hard 'ui' apps are to build. Incorporating webkit in a 'custom browser' might not be easy; but not undoable.

Yes, it's pretty much undoable. You'd have to compile webkit for Plan 9, which requires a C++ compiler, which Plan 9 doesn't have. There are some gcc ports, but I don't know how well they work. There are also probably a ton of dependencies. So a modern webbrowser is not really feasible.

comea c++ is available though it costs $50

Abaco (the browser shipped with Plan 9) has support form most of the HTML4 spec, but lacks support for things like CSS and Javascript (see: http://plan9.bell-labs.com/sources/contrib/fgb/abaco.pdf).

It might be feasible to swap out Abaco's HTML parsers and such with a "modern" rendering engine like Gecko or Webkit while retaining its webfs-based approach to navigating the world wide web.