Amazon's EC2 service offers a variety of Linux and Windows OS choices, but I haven't found a service offering a similar "rent by the hour" service for a remote Mac OS X virtual machine. Does such a service exist? (iCloud looks to be just a data storage service, rather than a service allowing remote login, etc.)
Such a virtual machine service would be very useful for testing software in a reproducible, "neutral" location.
Just to be clear, I'm referring to services similar to EC2's on-demand or spot instances, where the machine (or virtual machine) is rented per hour, rather than typical web hosting services that involve a monthly subscription.