We use MaxCDN on our web hosting site (
http://www.handsonwebhosting.com) and have done so for the past 4 or 5 months. The reaction from our user base was instantly noted and people complementing on the faster speeds from various locations. We're waiting on the Edge servers to come online in Australia as we have a big client base in Australia & New Zealand, but it's prove a very successful launch within the United States and our European customers.
The nice thing about MaxCDN versus many other CDN networks is that it's a PULL system. You don't have to upload your files to another location. It will automatically pull a copy and store it in the cache servers around the world. As long as the pages are being opened, the cache is available to the visitor. If there's no page cached, then it will pull the page directly from the site. No need to upload to another place, just set the subdomain and the A Record for the redirect and you're off and running.
The unique URLs I don't believe is possible at this time (that is in the works currently). Some of our clients have used Amazon's S3 system to allow password protection or time sensitive URLs (electronic downloads etc), but MaxCDN doesn't have this capability at this time.
We're huge fans of MaxCDN and use it on a number of our sites - very VERY easy to work with - it's one of those "set it and forget it" type setups.