I just got mine last week and have used it twice for a plumbing project:
1) cut grout line to remove a sink base
2) had to cut off a 1 1/2" to 1 1/4" ABS adapter in the sink drain pipe so I could switch it to 1 1/2" adapter (for a bigger p-trap
Also used it to clean up some of the cast concrete bits on the sink base (it's not your typical cabinet).
It worked GREAT. Depth stop helped to keep me from damaging drywall behind the grout line that I had to cut.
For cutting off the old drain adapter, did it free hand but used the dust collector, which kept it nice and clean.
Handles great. It is a little too easy to turn on the switch on accident, and Sedge addresses this in the Festool Live episode on it. Basically, get everything ready (dust, guide, blade, etc) on it BEFORE you install the battery.
Two nits:
1) I've found it a little difficult to get the battery installed all the way. You really have to smack/slam it on there for the final seating
2) Can't use the dust collector and the depth stop at the same time, unless you use a long blade with he plunge guide, which didn't work for the grout cutter.
Pictures attached. Overall, pretty happy with it. And it's a gateway drug! Now that I have the 18V batteries, the C18 is a cheap purchase! [cool]