Tovec
Explorer
We haven't made a lot of use of CMB/CMD in our nascent PFRPG game yet. What we have seen -- Acrobatics rolls to avoid AoOs -- have been instances where CMD is too high.
Technically, I think the "10" part of "10+CMD" is too high, but still.
My max-ranks rogue fails these against level-appropriate enemies about 50 to 60 percent.
I haven't found this to be true at all in my games with both a monk and a rogue having acrobatics. Both seem quite capable of getting through enemy squares or out of AoOs with the check quite simply. If they failed about half the time I'd be quite happy actually. It means with hard work and dedication you have a decent chance of avoiding something that would ALWAYS hit everyone else. It doesn't mean you have a PERFECT chance of avoiding the thing that ALWAYS hits EVERYONE else.
I will have to playtest further but I found the tumble (acrobatics) check in 3.5 was far too easy, any tumbling character I had could almost always get away. Now its a little harder so I'm happy.