I've had my Sigma SD10 for about 8 months now, and have over 2500 shots with it. I was an avid film photographer twenty years ago, but had really given it up for a while. The Sigma is my third digital, and first dSLR. The handling of the camera is generally excellent---there is no need to dive into submenus for any of the photographic functions that I use. Autofocus is usually accurate, manual focus is possible but somewhat difficult with the viewfinder. Battery life is reasonable with rCRV3's.
The images that come out of this camera are wonderful---due to the Foveon X3 sensor. Sharpness and a three-dimensionality are the hallmarks of the photos. I've had many people look at my prints and remark on how "realistic" they look---and this includes other dSLR owners. The images enlarge very well, and the fine detail really makes people notice. Learning how to shoot high ISO photographs can be a challenge, but getting the exposure right (and buying fast glass) is the trick. I've gotten good photographs at ISO 800.
The Sigma Photo Pro software that comes with this camera is also a treat to use---it's a very powerful RAW converter that really helps the images shine. I use this, iView Multimedia Pro, and PSE to process, manage, and print---and the workflow is pretty good.
Problems:
Multiple rapid shots in single shot mode are somewhat of an issue for my camera---has nothing to do with autofocus (because I turned it off). I may get a 0.5 s delay between pushing the shutter and it firing, but it's not consistant. Multiple shots in continuous mode are fine---so if I need to capture fast action I use that.
I would also like to see "cleaner" low light noise---finer grain. This is usually a result of underexposure---as a result of not enough light/slower lenses.