I used a script called crouton[0] developed by a Googler to install an Ubuntu chroot. I get to use Chrome OS as my browser (and it's a very good browser) and I get a fully powered Linux instance to develop with locally in crosh (and it's a very good-looking shell). I use vim, but if you want a GUI, it's very easy to install your DE of choice, since it's the same as it would be as any other Ubuntu machine.

I haven't run into any problems using it this way that many other people seem to have. Judging from online forums, many people install a chroot, Unity, and then everything falls apart for them because Dropbox/Sublime Text/something isn't ARM compatible. Sticking with just a browser and a CLI has made development on the Chromebook simple.

[0]: https://github.com/dnschneid/crouton