iostream vs. stdio

so, I've got EXPERT PROGRAMMERS telling me to use printf instead of cout in c++, ok but why? what is the difference (in b4 stream)

>>16
I actually haven't measured it, but I imagine cout is faster, or rather, has the potential to be faster. because printf interprets the format string, the cout stuff is determined at compile time.

Ok, yes, it's not a huge overhead. I'm a moron, forget it.