cool service to test website on multiple browsers/os

I discovered a cool little service that you can use to test how your websites behave on many different browsers and several operating systems. It's called CrossBrowserTesting.com. The service starts off free, limiting you to 5 minutes each session but unlimited sessions. This is usually good enough to give a website a quick once over or to test some specific functionality of a site.  

You log into the site, request a session, pick which operating system you want to work in which determines which browsers you'll have access to, and then using a VNC like interface directly in the browser window, you get access to the system desktop where you can open which ever browser you like and load up your website. 

If you need more then 5 minutes a session, you can buy 5 minute block intervals starting at $1 each. If you buy them in bulk (starts with 6 or more) the costs go down.

I think this would be an invaluable service for any web developer/designer.