I basically echo the sentiments above. I've been to PP before/after (but not during) the Ranariddh/Hun Sen 'election' fiasco, and have seen a steady increase in security and safety. Visa-on-arrival at PP has been very doable for awhile, so you don't need to waste time getting a visa beforehand.

Do watch for the beggars and pickpockets though. I'm surprised that they haven't been mentioned already in this thread. Typically you should be very wary of young kids, or women carrying babies, especially around the Russian market and Toul Sleng prison. Otherwise, if you stick to the main areas at night (e.g. along the Tonle Sap river), you should be fine.

Enjoy.