I rate the viewfinder of my P645N above all the other cameras I've got or have owned, and this includes Nikon F5, D300, Pentax LX. The ergonomics of the camera are really superb. The one lens I have for it is the SMC-A 35mm f/3.5, also superlative (one of the sharpest optics going, at any price, and this one was cheap). If there's a mechanical weak link it's been that the shutter dial has popped off a couple of times, I glued it back on; there's a fellow selling shutter dials new for under $25 on ebay.
P645N doesn't like to run off of NiMH rechargeables, which AA batteries I use with practically everything else. So instead I use lithium cells and they last quite a few rolls and a long time.
The slow shutter sync speed can be an issue if you do portraiture... 1/60th. The P67 is worse at 1/30, dreadful, actually, outdoors. There are a couple of leaf lenses for each that sync to 1/500.