[nicholassmith]

I can think of a couple of practical uses, the biggest one that comes to mind is helping places like CodeSchool do in browser PHP tutorials with the code actually executing. So definite practical uses :)

[andreasklinger]

This an very valid reason. The other one could be user-frontend editing of wordpress widgets or similar little nasty diy codebits.

[jqueryin]

Great use case, might I add.

[koglerjs]

As someone whose initial reaction was "God why?" I stand corrected--that's an excellent use for this project.

[nicholassmith]

Must admit I had the same reaction and then it clicked and was much more impressive.