I just tried to talk about this.
http://www.dakkadakka.com/dakkaforum/posts/list/210629.page
I will be taking probably three in a 2000 point chaos army, for just that use. I honestly just don't like using raptors. I think they are boring. I liked them better when they had extra rules in the last book.
But other than that, you are better off with Raptors.
They ARE fearless, which makes them perfect for that role.
I'm also curious what they could do. Just what you say, tying up squads. The most important thing to do is use their fast attack final deploy to make sure they aren't going to be led around by the nose the whole game.