If you define a bust as a player who starts (is his team's primary starter) for three or fewer seasons, then
from 2002-2007 only thirteen players busted in the top ten, about two per year. And teams are doing a far better job rating talent at the top of the draft now vs. ten years ago.
It's significantly lower in the rest of the round, but a lot better than a coin flip until about the third round, when it's pretty much a coin flip whether you get a roster piece or a bust. After that, good orgs typically do better on Day 3 than poor ones, but no one is consistently pulling 50% after that.