Performance/Speed
Trade down from a DSLR, and universally, you'll lose speed. Both the Canon G9 and the Sigma DP1 have lenses that telescope open when the camera is powered up, which is a significant part of the startup delay.

The G9 delays 0.6 seconds between when the shutter release is pressed and when the actual exposure is captured. The DP1 gets its shot taken in a considerably more languid 1.5 seconds – the delay makes the DP1 completely impractical for moving subjects. The Sigma DP1 manages bursts of three shots in 0.7 seconds, shooting either RAW or JPEG. The Canon G9 shoots bursts more slowly, but is set up to go on apparently indefinitely. It shoots one JPEG roughly every 0.7 seconds until you get tired of holding down the button. In RAW+JPEG mode, which records both file formats, it shoots frames at intervals ranging from 1.9 to 2.5 seconds, and again, it just keeps on chugging. The odd thing is, it's possible to shoot frames that fast in single shot mode as well.