A good choice for serious photographers.
I had the prosumer Canon PowerShot G1 for 3 years which was great fun, but I wanted better image quality. I particularly like taking things like sunsets which it simply couldn't handle. After looking at various DSLRs I decided that the SD10 was best for the type of shots I like to take. I've very happy with my choice, though I had to go through a fair bit of learning in getting used to SLR cameras, compared to "auto" (consumer orientated) cameras.
The Sigma SD10 gets a lot of the hard stuff right. The sensor is stunning and photos look great on screen or on print. This is significantly aided by the free Sigma Photo Pro RAW processing software, which is very usable and very useful. There is no in-camera JPEG option, but I consider this a non-issue, even though I never used RAWs before.
The SD10 body is nice and easy to handle. Switching between settings is easy. I can even use it quite easily while wearing gloves. It is also very fast to turn on and use - almost instant.
After using it for so long (nearly 5000 photos at time of writing) you do notice areas where things could be a little better. These are not real flaws, since with a bit of experiance or work you can get around them, but this is what stopped me giving it all 5s:
*) CF writing is somewhat slow. This is camera limited and not card limited - any CF faster than 10x is not worth it. Given the file sizes are often 5-8MB this is a bit of an issue. For the types of photos I take, this is rarely an issue however.
*) The SPP software should have built-in image clipping options, being able to view the whole image at 100%, and better options for saving for large prints.
*) Auto-focus could be a bit better, though this is somewhat dependant on the lens. Tracking moving objects, shooting in low-light situations or when there is not much detail in the center can be a bit awkward.
*) The eyepiece could be bigger, and should have the ISO setting in there (along with shutter speed and aperture).
*) The RAW processing could be a bit faster. This is more of an issue for laptop users though.
Despite these issues, I still gave it 5/5 for ease of use since other features are truely excellent and make up for the above.
In summary, I would say that the fundamentals are very sound. The rough patches are small and manageable. In my experiance, this is rather typical of a small but excellent engineering team. With software improvements (SPP 2.1 just came out), the fundamentals are improving while the rough patches are getting slowly stamped out. This makes me rather hopeful for future Sigma DSLRs.
Problems:
Unfortunately, the camera did come with some dust on the sensor. The best way to solve this is to get both the sensor and chamber nicely clean - once you've done this, the dust protector does work and I've seen no new dust in 4 months. Simply cleaning the sensor is only a temporary solution since there's still dust in the chamber.
With 4 AA batteries, the battery sensor / power can be slightly flakey. Solution: CR-V3s or the battery pack (double size). Shame RCR-V3s are still not mainstream yet.