I'm currently considering a swap from P25 to P30 just for the useable 800 iso and the speed increase in shooting. The inconvenience of larger file sizes for no resolution increase together with a smaller CCD are the two drawbacks that spring to mind.
I have a loaner at the moment and I'm getting attached to it already. I'm shooting fashion tomorrow, a wedding on Saturday and I'll have shot about 1000 frames by Tuesday with all the H1 lenses. I'll see how the new crop affects my shooting style. To be honest I'm expecting to like it, Just like I did with my first dslr 6 years ago. I rarely need all the 35mm lens's image so I'm happy to have the crop. My 210 will be more like a 250
I've read about the P30 being soft. I think the smoothness of tone and lack of noise is causing this apparent softness. I did an extensive side by side comparison today at 400 ISO and I recon the P30 gives a more pleasing look but you have to switch off the noise supression to get all the detail.
I'm not sure which back is the most expensive the P30 or the P25. I think if I was starting from scratch I'd go P30. If the P45 had microlenses it would be my choice.