Update: May 5, 2014 Molly is now providing custom product demos to businesses. You can still view some of the demonstration videos to get an idea of her work. The post below is an historical record of the web site as I viewed it in 2009.
I do visit review sites to check out products and services. I like it even better when I can see the product in action. Demo Girl provides screencasts demonstrations of applications and software.
Demo Girl are actually two sisters, Molly and Maureen McDonald. In addition to creating screencasts for their blog, they also provide services to companies making videos that demonstrate client product features. They do disclose when there is a commissioned video used on the blog.
Demo Girl serves their blog visitors with information about new products and services and they get the opportunity to market themselves to potential clients.
This is another example of how people are creating information products. In this case, the reviews and video demonstrations are being used to display skills that businesses might want to contract or purchase.