tedster - 3:28 am on Nov 19, 2009 (gmt 0)

It doesn't even need to be separate domains - just separate hostnames (subdomains) will allow more simultaneous browser connections, too. The link I gave above for "best practices" says this:

Split Components Across Domains tag: content Splitting components allows you to maximize parallel downloads. Make sure you're using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org and static2.example.org