I don't have one, but recently tested a Sigma DP2 in a shop.
Very good results in low ISO settings (< 100 ISO). Probably better IQ than concurrent systems (Ricoh GR, Lumix GM1).
At higher ISO, the advantage is less evident.
Seems quite slow as well (minimum interval between 2 photos in s continuous sequence)
If you have a specific question or test to do, I can probably check with the people of the shop.