The Plan 9 environment takes some acclimating. Many of the commonly-found UNIX utilities have been replaced or removed (there's no vi and no emacs), and the user interface relies heavily on mouse usage. In fact, a three-button mouse is strongly preferred. This might be a little strange if you're a hardcore CLI person. It took me some time to get the hang of it.
I recommend going through the READMEs for Rio, the Plan 9 Window Manager, and Acme, the programmer's editor. I found the Plan 9 Newbie Guide (PDF) and the RIT Plan 9 Introduction to be very useful. There are also a few helpful youtube videos: