Separating your site across multiple servers/subdomains
 

While this seems like a good idea on the surface... preventing an entire system from going down all in one shot... it's annoying as hell when I load a page and have to wait 5 minutes for img.yourdomain.com to time out.

That ONE IMAGE at the top of the page that uses it is preventing me from loading the entire page.

This isn't directed at anyone in general, I've come across many sites like this.
If you're going to use this method, take care in it's implementation because it can be frustrating as hell sometimes.

:2 cents:

That is why I insist on hosting other people's banners on my sites. Hotlinking is too risky.