boneprone's right - more than 3 to 4 is proabably overdoing it.
a1ka1ine, I agree that popups are annoying but I must say that I think it's a mistake to just dismiss the possibility of using exit/entry popups just because you find them annoying, personally. Ignoring a potentially large revenue stream due to your own personal tastes just doesn't seem like a good idea in this particular business.
That's just my

though - I don't think there's a "right" answer to the question. I just know we make good money off of our consoles, so we're not likely to drop them anytime soon.