I've played around with a couple different builds and I think it ultimately comes down to your play style.  From reading all the posts, I guess I am one of the rare players that uses the Demon spec.  I only went in far enough to pick up Soul Link and Demonic Knowledge. The rest of my points are in Destruction where I had enough points to get Ruin.

As much as Affliction is wonderful in PvP, and for as cost efficient as it is, I still raid more than I PvP.  And dotting up bosses in raids is the epitome of boring for me.  I like seeing the crits flash across the screen.  And I'm not interested in the high threat fire spells that you can really bolster in the Destruction tree.  So I guess I've made a hybrid build and it works for me.