Who is Hosting This?
I just found a cool service that identifies the hosting provider for any particular web site: www.WhoIsHostingThis.com. Although there are a few similar services out there, WhoIsHostingThis digs a little deeper to find the actual provider even if they're built on another cloud provider's infrastructure.
Note that some other identification services identify Amazon Web Services as the provider for Acquia-hosted customers. This is because we use Amazon's highly-scalable Elastic Compute Cloud (EC2) for all of our customers.
WhoIsHostingThis also features a customer review section. Acquia Hosting's review page is here.