I don't crumb coat on my cakes--ever. I never had a problem with crumbs until I tried the icer tip. Arfter the first few failed attempts, I posted a question here and found that the icing I was using was too stiff. Even though it was the exact same icing I used for my "slap -n- spread" method. I thinned it out a bit and it works great.
Takes some getting used to, though. If I'm just doing a little cake--I use the old fashioned method.