Would/Do you use Cloud-based IDEs?

I'm wondering what people think of using a Cloud-based IDE such as shiftEDIT.net or cloud9ide.com.

Have you found it useful? Do you like the idea? Would you use it?

I'm asking as a developer looking at different tools out there.

While the idea is enticing - being able to use the same IDE where ever I have access to Internet and browser - it seems like these IDEs are missing support for back-end technologies like Rails/Node.js/PHP/etc.

What do you folks think?