I received my copy of the SD-15 in July 2010 after waiting for it for 2 months. It came with over 1000 shots already in the shot counter, but with a new camera warranty from Sigma USA. Don't settle for anything less than a totally "legitimate" purchase from a real dealer. I didn't: the Sigma USA warranty was the important thing. When I got it, I also got a Sigma 50-200 F4-5.6 OS lens for what I thought was a too-cheap price of $169. What an excellent combination this turned out to be!
I was really waiting for the Sigma 17-50mm F2.8 OS lens, but did not receive it until the end of December 2010 (Sigma-mount availability issues). Because of focus problems I ended up sending both camera and lens into Sigma USA service for (I guess you could call it) lens calibration (they had it back to me in a week). No such issue with the 50-200 F4-5.6 OS lens though, it was perfect from the beginning. After Sigma makes any lens for everybody else they make it available for Sigma cameras, so you need to cultivate a little patience (well worth the waiting). Go with OS (optically stabilized) lenses if you shoot in less-than-daylight conditions, since the SD-15 image quality does not hold up at speeds higher than ISO 400. My next (and possibly last) lens will be the Sigma 85mm F1.4 (I'm simply running out of money).
If you are willing to shoot raw (don't use the in-camera JPEG) and process the images with Sigma Photo Professional (free download from Sigma), you can get stunning results! I was not surprised by this because I started out with a Sigma DP2, which in my opinion is equally capable in the image quality area except it does not have an interchangeable lens. You also have to be willing to "fiddle" with either camera to coax out of it the best exposure, focus, and so on. Since I am a hobbyist and I enjoy this sort of "fiddling" I am very happy with my SD-15. The quality of the images makes it all worthwhile.
Sigma won the megapixel wars by making a better pixel. The images resize very well to 4x JPEGs in Sigma Photo Professional (sigma calls it 2x) because there is very little (if any) visual chaff in the basic images. I've had 18x24 posters printed and there is plenty of detail along with the excellent colors. By the way, Popular Photography Magazine reported a test result of Excellent for color accuracy, in its SD-15 lab test of January 2011.
You might want to wait for the Sigma SD1 if you regularly print larger than 18x24...