At CSSIgniter we use MaxCDN for about a year now at both our main website and each of our 66 WordPress theme demos (66 at the time of writing). We serve literally millions of static files and hundreds of gigabytes through MaxCDN’s servers each month. A CDN is probably the first thing a developer or website owner should implement on his website if he’s serious about his business, due to how cost effective it is (MaxCDN‘s plans start at just $9/month) compared to the benefits it gives.
On Envato’s theme submission guidelines
A couple days ago Envato announced a new set of theme submission guidelines for the Themeforest marketplace; you can read them in detail here.
They are a set of rules in an effort to ensure that every theme provided by Themeforest meets a certain high quality standard, using clean code and general web development best practices. We believe it really is a great list of what to avoid and what to be careful of when you develop a WordPress theme and a website in general and Envato has done a great job in recruiting experienced authors and advisors in order to compile it.