Immensely frustrating. Two problems with them.
One:
The insistence in wedging one ankle into another, consistently, no matter what you try:

I mean you can see from the picture that the other leg isn't exactly hidden from view :( Two hundred frames in a row it's insisted that the legs are there. Two hundred!
While not a complete disaster for me personally, as most of the mocap I do will focus on torso/upper shoulders, it annoys me that I've got a clear capture of the actor and yet the software insists that one ankle should be firmly embedded into the other. Plus it erodes my confidence that the mocap won't suddenly freak out in unexpected ways. I have tried:
IK'ing the leg back out straight and refitting the pose (hah! says the software, I think you'll find her leg is here!)
Adjusting the model appearance several times in several different ways
Changing the ambient lighting
Redoing the calibration a couple of times
Enabling foot tracking
Disabling foot tracking
Putting down a light coloured sheet for the actor, in case the dark carpet was interfering with the dark leggings
All to no avail.
Which leads me on to problem two:

That's four frames in a row. My actor hasn't moved. What the hell? I guess it does freak out suddenly in unexpected ways :)
I mean sometimes it loses track of an arm and I can IK the arm back into place and chances are it'll recover. Fine with that. This leg thing though?! I can see the damn leg onscreen, it's there - arrrgh!
I've got four hours of mocap to process that this girl kindly gave me her time for, and a lot of it does involve moving/sitting so I really want this to work! I can sense it's close, but I want it closer :)
-Ian