Concept: 2 out of 5
Execution: 2 out of 5
Yeah, but: Not bad, but it's nothing to write home with.
The Long Version: I bought this because I wanted a nice pen, and I know that Caran d'Ache makes good ones. I know this because Rado, the Swiss company that makes scratch-proof ceramic watches - so they'll never look worse than they do on the day you buy one - had some as promotional items and I snagged a couple of them. Caran d'Ache is also Swiss, so it keeps it all in the family.
A lot of people use my pen in the course of a week, and the most frequent comments I get are about how small my pen is, and how slippery my pen is in their hand. I'll admit that my model 849 is smaller than average, but it fits my hand and it's easy to carry in my pocket, so it suits me just fine. The slipperiness is a problem that I have to agree with: it can be hard to use when I need to write on carbonless paper, and I often find that I need to grip the shaft so firmly that my hand starts to cramp. If I'm writing with a more relaxed grip the pen is comfortable, but the legibility of my writing isn't something that's improved by being fast and loose.
From the photos on the maker's web site, I think I have the glossy-finished "Metal X" pen. The Rado promo pens - I eventually found them packed in a box from my last move - have a much more comfortable matte finish which gets rid of the grip problem, and it doesn't detract from the look or carrying convenience of the pens. If you have a choice, pick the more textured finish. If you don't have a choice, you might want to skip the smooth version. They look very nice, but ultimately I prefer my buy-it-by-the-dozen Papermate Comfortmate Medium to write with.
updated February 2013: four years later, I have an update.