"Powered USB" goes up to 12 or 24V, but that's another thread. http://www.poweredusb.org/faqs.html
I almost never turn my PS3's off-- they donate to Folding @ Home when not being used. So as long as the 4308 will power the PS3IR-PRO properly, then I think I'll be fine.
I just timed the Denon, and the USB ports have power in ~2 seconds after power-on. I already have 14 seconds of delay in my "power-up" macro for all the other equipment, so no worries as far as the time is concerned.
If I ever did want to power-down the PS3, that's also not an issue, since I can put almost unlimited amount of delay into my URC remote.
I noticed another person here with a Denon receiver who was having issues. So I hope this Denon works, but if not, yeah, I'll just use one of my USB chargers I have laying around...
Has anyone here tested a Denon 4308 to power their PS3IR-PRO?