I'm going to just leave my PS3 Skyrim on and let time pass for a while. Was the reset time an in game month, or longer?

I believe it's 48 game hours. When the game was working for me, I was power leveling my blacksmithing in Whiterun by buying up all the iron ingot. It reset every 48 hours for me.

Yeah, I can echo Tenebre81's statements. When it's working correctly, venders reset at regular intervals. But as we all know, something can work correctly (or not) from the beginning with this game and at any time, take a turn for the worse.

I heard a Month to reset some items like bodies in caves and what not.
I did the Companion quest (the last one) there were items in front of the place in Whiterun and when I came back from the quest they were gone MAYBE some of the NPC moved them no idea. In caves items remain for days/weeks. Not sure if they ever reset.

I dropped items there cause I could no longer carry them. Since I don't want/need them anymore the game should just purge them from the file.

48 hours on vendors for sure as I wait exactly that long in order to sell-off my loot when they run out of cash.