A Google Webmaster Help thread has a Webmaster concerned that since switching to a content delivery network (CDN) his pagerank and search rankings declined.

A CDN is a way to host your site or parts of your site on servers that are more scalable in terms of server resources and bandwidth. Many large sites use CDNs to host graphics, videos and to scale up their database resources when needed. That being said, are they bad for search engines?

The answer is, it depends on how you have it configured. Google does index files on clouds and if you host files on the cloud properly, as described here you should be fine.

That being said, JohnMu from Google replied to the webmasters concerns:

Overall, CDNs are fine as long as they are configured properly. They can actually lead to a faster site, which we all know Google is looking at.

Forum discussion at Google Webmaster Help.

Update: I have a new post named More Tips From Google On Content On CDNs.