I don't have any comparison photos for you, but I can give you my impression of both cameras. I seriously considered the Sigma DP2 for months before I finally chose the Panasonic GF1. I never owned the DP2, but I handled both, took sample photos, and played with RAWs in Sigma Photo Pro and Lightroom (respectively). Just some of my thoughts about each one:
Sigma DP2:
- Feels slightly smaller, plastic, but solid
- Acts like a compact digicam speed-wise. Not as horrible as reviews might have you believe, but not in the same class as the GF1
- Wonderful color in photos (low ISO), but not very accurate color. Able to pick up very subtle tones though
- Lower resolution compared to the GF1. I compared DP2 sample photos to some that I took with my 5MP Sony V1 and the DP2 was higher res, but not as big of a difference as I was expecting
- ISO above 400 gives splotchy color (usually unusable), but nice converted to B&W.
- SPP is slow and clunky software. I'm under the impression that it is still the best RAW converter for Sigma cameras, though maybe others have caught up now. In any case, try your RAW converter before you buy.
Panasonic GF1 + 20mm:
- Solid metal feeling, feels higher quality but a bit larger than the DP2
- Reacts like an DSLR to me (coming from a non-DSLR, it is a BIG difference)
- 20mm f1.7 is very fast in focus and great for low light shooting. Very sharp lens, and provides more light than the DP2's f2.8
- The 20mm can give you greater background separation for portraits (more defocused), compared to the DP2.
- High ISO performance is much better, and combined with the 20mm gives great low-light capability
- Interchangeable lenses means that I can try out other ways of shooting in the future
Overall, I'm really happy with the GF1, and I think it's a better choice for most people.