I have been trying every possible method for creating CSS content boxes and none have been as simple as this.
It’s beautiful when it is working.
Roger Johansson is well respected and it’s bound to be a good method 
The ony problem I have with JavaScript corners is that on large sites the delay is unbearable and slows the page down. Indeed I used similar routines on a large site for a client but in the end had to remove the javascript and go back to css and images as per usual.
For small sites and for small numbers of corners it would be great though.
A better compromise would be to to use border-radius (-moz-border-radius/-webkit-border-radius) for modern browsers and supply only IE8 and under with the javascript.