Quite often, I see web sites that draw resources from multiple domains. Made up example: Foo Bar Ltd has a main web site at foobar.com, which references files at fbltdcdn.com and foobar-rewards.net. ...
I've been arguing for some time about this topic, now I'd like the opinion of professionals. My point is that a domain should be made of 2 or 3 levels at most, like: mysite.com blog.mysite.com ...