Well, between the problems with school last year, the rounds of testing, and the homeschooling, not to mention having a very socially aware and curious child who could read the covers of the books about GTness that I was bringing home...we sort of had to talk about it.
We told DS7 pretty much the same thing that MON said, also. We did stress that this is not something to brag about, any more than one should brag about the color of one's eyes or the length of one's legs. It's just part of the package some people are born with, and it's not how smart you are but how hard you work that matters anyway. We are pretty matter-of-fact about GTness around here.
I also regularly repeat to the boys the mantra my mother taught me:
"It's nice to be smart, but it's smart to be nice." That's a biggie. Being smart is no excuse for bad behavior of any sort in our house. If anything, it means that the expectations for good behavior are even higher. Good manners are required and thoughtfulness is necessary.
If I may brag about my kids a wee bit...parents and kid-friends alike think they're really sweet boys, so I don't think that telling them about GTness has done them any harm. (The 7yo has needed to talk more about GTness than the 4yo, of course, just to be clear.) To be honest, I'm always a bit amazed at how much other parents rave about them. They're kids who always seem to be in the "welcome to come over anytime, even without their mom" class of friends. It's nice.

They do seem to be pretty well-adjusted kids, if I do say so myself. As always, though, I take no credit...mainly because I don't want to take the blame if they screw up!

I only say this to show that talking openly about GTness doesn't seem to have automatically turned them into conceited jerks!