Took three of the middle sizes up the Triple Direct. All the pros have been listed above, so instead I'll list one pretty serious con for all you aid climbers: the stem design (with tapered, pastic, protective aspect) is so thick that, in the smaller sizes, you can't see around the side of it to evaluate the placement of the cams. This became a problem several times, and I'd switch out for a small Alien, whose stem is narrow enough to see around no prob, or TCU, whose u-stem lets you see in between.
Still, you'll notice I gave these four stars, and that's not for nothing. There's just something intangible about BD cams...

Good places, both in horizontals and cracks. I was thinking about getting some TCUs for the above mentioned situations, but will likely but these guys instead. The best part is the flexible, protected stem and narrow profile.

Looks good but placements are not so solid as one would think.
Oh they look so nice, so light, yet when I needed to bail on a trad pitch, I placed a piece, (aid like, with body weight not fall factor) in the direction of load the head deformed. I found the wires to the lobes had also started to bend open. This was the double zero. Why a three if so bad, the zero's and up are just fine and my prefered; below zero rather use TCU.

I finally had a chance to use the C3's in "real life" this weekend. My friend had the 0, 1 and 2 sizes and we climbed in the Valley.
Everything that others have said is true. They are beautifully made, have a great feel, are super narrow, etc. I was particularly impressed by the springs. Each cam is really positive when placed. They felt really secure. I would love to try the 000 and 00 for aid. I'm sure they'd fit into placements where no other cam could.
The one downfall I could find is that the little metal things coming from the axle are pretty long. On sharp, shallow, horizontal placements, those things could get bent. (I didn't fall on one of these placements, but it seemed like and obvious point of weakness.)
Another problem I have is that the 0, 1, and 2 are the same size as my blue, green and yellow aliens, which I will never give up in a thousand years. Throw in the high $$$ ... I'll leave it to the rich new guy to supply this rack.

The stiff springs and clean design are confidence inspiring.