Browser-Based IDE

CodeRun Studio is a browser-based IDE that currently handles PHP and ASP.NET. Frankly, I don't get it: the only advantage I can see to doing development on a remote server via a browser is the ability to switch rapidly between platforms for testing purposes, but the same virtualization technology that makes that affordable also lets me switch between VMs locally. Several developers I work with already switch between Mac OS X, Windows, and Ubuntu Linux on their laptops as easily as I used to switch between virtual desktops, and if the GridCentric people have their way, doing so will become even easier. I had the same reaction to Bespin, so please: what am I missing?