I've tried a lot of testing services like this, mainly web based ones that either take screenshots of a virtual machine, or allow you to remote control a virtua

I've tried a lot of testing services like this, mainly web based ones that either take screenshots of a virtual machine, or allow you to remote control a virtual machine with a web browser. You really don't get a feel for the performance and responsiveness of a browser unless it's in real time and latency free. A lot of the services I've seen also have to have the page available on a web server for them to be viewed, which isn't optimal when you are attempting to make tweaks. I've found it a lot faster and more effient to use VMWare Fusion and a series of prefabricated Virtual Machines. A couple of installs of OSX (you'll need to patch VMWare to get around their restrictions) and Windows will get you a very nice testing suite that can handle a variety of configurations. The main caveat to virtual machines—licensing aside–is that you'll have to store a very large amount of data to have them all running. I've around 8 installs that I run at least once a week, totalling over 100GB. It won't break the bank, but it's something to think about if you are resource-limited.