I was in PP a few months ago. It's an interesting enough city for 2 or 3 nights but I wouldn't want to spend much longer there. Get a tuk tuk driver to give you a tour. For $US 10 you can have him for most of the day.

The strip of bars and restaurants by the river is a fun (and safe) area but otherwise it's not a city you can wander around at night. The best bar/restaurant for people watching is the historic Foreign Correspondents Club (FCC) http://www.fcccambodia.com/phnom_pen...ique-hotel.php - especially during the cocktail hour(s) at sunset.

For a hotel, I'd recommend The Pavilion (http://www.thepavilion.asia/). The rooms aren't especially luxurious but the building is fantastic.

PP is certainly developing quickly. Now is probably a good time to go as in another 5-10 years it'll be another Bangkok in the making. What really hits you is what a young place it is. For obvious reasons, you see very few people over the age of 40 or 50.