I guess that it is a matter of what kind of images you take and in what context.
Jack and Mark seem to think that the battery life of the P2000 is good enough for their usage.
I typically hike 2 to 7 days away from my base, and find the 8-10 GB autonomy provided by the P2000 to be really too limited. Make no mistake, I also used to own a Vista that was completely unusable... The Epson P2000 is way better, but still not good enough FOR MY usage.
The way I use mine also drove my decision not to take a backup along in order to save on weight. If I were to take a backup along, I would probably buy another P2000.
As far as display is concerned, I find the 640*480 display of the unit to be best in class, but the way it displays the .nef of my D2X is not completely satisfactory. Color banding is present often, and makes me think that the image used for display is probably coded on 6 or 7 bits only. I don't find this to be a problem though since I hardly check the unit in the field... battery concerns again.
If you really want to do thorough checks of your images in the field, I would still recommend a light laptop. The IBM X40 I have been using for a bit more than a year is great and features a 6 hours battery life good enough to download tons of GB. Its Pentium M processor is too slow for PS and NC though...