Here's my take on the P5's. I have had them for about a month now and have no intrest in replacing them.
They definitely do have a unique and colored sound signature, but one that i thoroughly enjoy. They dont do everything right and not all songs sound very good with them (some really sound awful, but very few), but for the majority of the music i listen to the P5's handel them very well.
These are definitely meant to be used un-amped and for this purpose they shine. IMO, the P5's produce some of the best un-amped portable sound i have heard. I hands down prefer them to my d1001's. You can certainly get better portable sound but not without an amp IMO.
As for comfort i find these fantastic. I have no problem wearing them for 5+ hours. They did start out a bit uncomfortable, but as the headband loosened they quickly created the perfect clamping force. For those having trouble with the clamping force i would suggest trying to bend the headband open a bit.
These certainly aren't for everyone, as i have seen from these forums. They seem to resemble grados, NOT in sound (please dont jump all over me for this) but in the fan base. Some people love their sound and some hate it; some think their SO uncomfortable and some think they are top notch comfort.
But for anyone curious about them i would suggest buying them and trying them out. If you dont like them you can take advantage of apples 14 day return policy.
Anyways, just my thoughts.