Hmmm tough question Gordon but as a DSLR owner who might be looking for a compact I have to say I wouldn't buy the DP1. I think Sigma has done a great job of showing that it can be done but there's a long way to go yet. I think most DSLR owners who buy a compact do so for the added convenience they offer. The DP1's lack of any zoom, even a simple 3x, intelligent auto mode, poor screen in low light and poor feature set when compared to other compacts, such as the G9 or FX500 means that there is too much of a compromise for those looking for 'out of the pocket flexibility'. These downsides could have been overlooked if the performance turned out to be as good as Sigma said it would - sadly this is not the case and the lack of even a 1600 ISO option is a major killer for me. Also, the unacceptably slow handling is another major downside. Again, if the quality was there, I might consider it.
Well done Sigma for hopefully opening the floodgates but the first try just isn't good enough to be worth the money in my opinion. I'd much sooner spend my money on the G9 or one of Panasonic's models because I think I might leave the DP1 at home even more than my DSLR out of sheer frustration.
Of course, your review was fantastic and fair as always Gordon, good work.