Depends on the car really.
My mate had a new Elise and he was forced to not go over 3k for 800 miles, then 4k for the next 200.
I say forced, if he did excessively it'd have shown up on the print out they did at the 1k service, bye bye warranty
I had this discussion with a friend at work last week, a modern engine once warmed up on a run will be fine to drive as normal. Engines that are driven more lively from the off tend to produce a bit more power, rev more freely, and generally loosen up a lot quicker. Ok the risk is in later life the engine will develop problems earlier, but as said with modern manufacturing techniques this shouldn't be too much of a problem.
On the Clio forums people always say that 172s that were driven "normally" from the off rather than being driven like a girls blouse do drive better, but if they've been mega thrashed from the off I wouldn't like to be owning them in later life. And that's the other thing, it's highly likely that by the time the engine does show signs of a fault due to this, I doubt you'll still own the car
The chap who I told all this too wasn't too sure, but today he told me a little story...
His housemate runs a courier company and for part of their fleet they use these Citroen Picassos. One has always been wragged senseless from day 1, when it was picked up the guy wheel span it out the car park, it's always being driven to it's limit. The other is not, it's driven sensibly and carefully most of the time.
Driving the two back to back he said that the thrashed one was noticebly quicker, felt looser and generally just faster. However other components had taken abuse and not help up so well, the suspension and brakes he said felt like a sack of spuds, but the engine felt great
