If you are looking at hosting very large wordpress sites you may want to look at wordpress mu, multi user edition.

http://mu.wordpress.org/

This version allows multiple users to each have their own blogs, and with an additional plugin, they can even use their own domains. You can host 100′s of blogs or even 1000′s on 1 domain or 100′s of domains.

Also if you are looking for a place to store images and other uploads check out Amazons web services. Amazon S3 is storage for the Internet. It is designed to make web-scale computing easier for developers. Amazon S3 provides a simple web services interface that can be used to store and retrieve any amount of data, at any time, from anywhere on the web. It gives any developer access to the same highly scalable, reliable, fast, inexpensive data storage infrastructure that Amazon uses to run its own global network of web sites. The service aims to maximize benefits of scale and to pass those benefits on to developers.

http://www.amazon.com/gp/browse.html?node=3435361

Also they have the elastic computing cloud. Amazon Elastic Compute Cloud (Amazon EC2) is a web service that provides resizable compute capacity in the cloud. It is designed to make web-scale computing easier for developers.

Bradford Knowlton
http://x86Virtualization.com