[Jach]

CDNs aren't an either-or thing. It's common to fall back to a copy on your server if the CDN version doesn't load.

CDNs involve a big set of tradeoff choices you have to make, they don't make sense for every circumstance. I don't think I'd ever throw in "Use CDNs as much as possible" into an optimization advice list.

[nym]

Yeah, keep the dynamic stuff on your webserver, static stuff on the CDN. Part of the reason I say "as much as possible" is because I've seen significant conversion improvements by enabling a CDN.