While I have not been able to directly compare the image quality of my ZD to Phase, Leaf etc, I tend to think that Michael's conclusion in his ZD review sounds reasonable. That is, the ZD may not be quite up to P25 IQ, but it's very close. I'm certainly well satisfied with it.
For mine, the biggest drawbacks of the ZD are the shooting speed after the buffer is full and the review screen. The shooting speed until 11 frame buffer is filled is excellent, so if you usually don't take more than 11 shots in a burst, shooting speed is not an issue. If you do shoot longer bursts - and at times I do - then you discover just how long 10 seconds can be!! I sometimes do large stitched panos with bracketed frames - the sun would have set before I had finished. So I still use the Canon 5D for them.
The slowness of the review image appearing on the rear LCD I find to be an annoyance. I wish it were faster, but it's not a show stopper. The size of the review image when you have a histogram and flashing highlights displayed is a sick joke, but I find it just useable (sort of).
I doubt I'm giving away too much in other areas and I'm willing to put up with the speed and rear LCD compromises to get the bargain pricing of the ZD. But these things may be show stoppers for someone else.