Everyone probably knows this, but I Just found this out. This may help people who don't know about it.
If you have a complex character, and its rigged with a child bone layer, this might help you. Say that you made the head into that bone layer. Smart bones wouldn't work for the layer the way you would want it to...The bones would work, but everything you do within that layer would go into some other action instead of the SB action.
Rats...

There is a work around for this, and it isn't hard that to do (Oh Who am I kidding, animating is hard work!).
1. First, Just keep finishing your all of your poses for the your smart bones actions. Make sure that you are on the "all" tab on the Action window. If your timeline ever turns grey (mainline), something went wrong. Try to get it done right the first time so that you won't have to go back and do it. I swear, if you mess this up...
2. Next make another smart bone, BUT make it inside of your child bone layer instead of the parent. Set that up with the same angle constraints, start time, finish time...all that. This time, you have to change the name. What I do is put a number right behind the name of it with no space. If you add a space, AS is gonna assume that you meant to apply a different action to the same SB.
3. Now, Make sure you are on that SB new action you just created. Once you are there, go to frame "1"
4. Finally, copy your parent SB action from step "1" into your new SB action. Now everything within that Bone layer will work with smart bones.
But now you have 2 smart bones that could alter your character in ways that you don't want. This is simple to fix. Just keep your parent angle, and your child angle the same. Also, keep your interpolation the same. If you do that, you should be fine.
If you messed up on your poses, just delete step 2 own down, fix the poses, then repeat this all over again.
Welp, hope this helps.