large scale ipsec

Hello, Who here on this list has deployed IPSec or other comparable lower layer encryption in a large scale environment, or attempted to do so? I've repeatedly heard claims that doing so is not feasible (either operationally or financially), but I have not seen any specific studies, reports, numbers or anything else to support this. Of course I haven't seen anything proving the opposite, either, which is why I'm reaching out here on this list. What was your experience, and what alternatives have you considered? If your findings were made longer than, say, 5 years ago, what might have changed to change the results? -Jan