Never could get the hang of comping in earlier versions and used automation instead. LOLOL Lazy bugger.
I bought the upgrade soon as X3 came out for the comping feature. It had me.
i wouldn't of upgraded otherwise as I was already an AD user even though I love the zoom out on curve EQ.
Anyway I am getting the hang of it again as it has been over a month since I was on it much and it is a game changer for me.
 
 

I've been loving comping since the the first inception... Absolutely loving the newest changes!
Have only had a couple issues recently tho, tracing back (near as I can tell) to projects that have already had some moderate mixing/processing done, and then needed to revisit to add new vocal tracks.
Firing up the comping process (setting up a loop and hitting record) on both these separate projects gets me through 2 complete loops, but on the 3rd, X3 freezes, audio engine locks with a loud 'growl' coming through the monitors and, when I regain control (end task on Sonar), none of the takes/loops were recorded. Even the autosaved version only produces a pre-comp version.
Can't reproduce at will as of yet, but both times it occured it was on some semi-mixed projects, so I'm focusing there as the culprit.
My workaround thus will be to render any projects that have had some processing done that end up needing some extra tracks later...
If I uncover more, I will certainly post  :)