I've been planning to go with a Felguard raiding spec since I started my 'lock about a month ago, so I found the recent thread on Felguard raiding very useful.
However, there was something that puzzles me: All of the specs I've seen for Felguard raids put their leftover points into both affliction and destruction. This doesn't make sense to me, so I thought I'd bring it up for discussion.
If you put your extra points into Destruction, you're going to be spamming shadow bolts for the 20% shadow debuff, so you want as many criticals as possible. You'll likely be maximizing Demonic Tactics then. So why not put five points into Devastation as well to double your critical bonus? This would also give access to Destructive Reach for some burst threat mitigation.
If, on the other hand, you intended to put more points in Affliction, you wouldn't be as focused on criticals, and would probably put fewer points into Demonic Tactics. You could then get Empowered Corruption, Amplify Curse, and Nightfall. You also have some filler points in Suppression so you don't need to worry as much about +spell hit equipment.
Both of these seem more viable to me than a mixed Felguard build, so why is a mixed build the most popular?