Reynard
aka Ian Eller
What you're describing is, and pretty much always has been, standard operating procedure both for my game and for almost all the games that I have played in.
However, I think it can sometimes be difficult to engage in this kind of play when certain aspects of the rules can create unintended "unfairness" -- the CR system, frex. Look at the difference between the Night Hag and the Frost Giant in 3E. Both are CR 9 enemies, but where the frost giant might kill a front line fighter with a couple lucky rolls (at best), the Night Hag is really scary with special and spell like abilities that could easily result in a TPK if played "to the hilt". I'm just saying that assuming the 4E design team met its goal of evening out this problem -- not to mention the problem of disparate PC power levels based on optimization -- the DM actually has more freedom to go all out on the party while still maintaining a sense of fair play.
In any case, I think the idea has enough merit that I am going to explore it. Look for a blog entry in the next few days.