Looks like it might be a pre-caching bot for networks.
"Mirror Image Internet, Inc. eliminates the "world wide wait" by providing
content delivery network services that result in faster Internet content
distribution and improved quality of service, delivering significant cost savings
for all Internet Service Providers, Content Providers, and enterprises. By
deploying an open standards network of highly scalable content delivery nodes
at key Internet exchange points around the world, Mirror Image adds a new,
high-speed, infrastructure layer on top of the Internet. This broad global
network intelligently stores content closer to the end user, and powers Mirror
Image's family of instaDelivery Internet Services. In addition, with cross
connectivity into key points of the Internet infrastructure, Mirror Image
enables fast delivery of 75% of all Internet traffic to millions of end users
worldwide - at rates of up to ten times faster than traditional traffic flow...."
And blahh blahh blahh...
Tell me though, why would you have a pre-cashing bot with a user agent like that?
Here is their home site [mirror-image.com].