I don't know, but it could affect sales less than used game sales do.

it depends on the platform.
for psp piracy is staggering - though i think sony started to ban modded psps from psn. you can't use psstore or play games in infrastructure online modes eventhough you have original copies - at least i can't log to my psstore acount anymore via psp and can't play Syphon Filter: Combat Ops via infrastructure. i wouldn't be suprised if 30-40% of psp owners pirated games, same goes to ps2.

thanks to RRoD and bans i doubt many people moded their 360s though there is probably 1-1.5mln in total. same goes to wii and ds but here it's because you really need to know what you're doing if you want to play pirate copies on nintendo platforms and most of wii/ds userbase don't even know that you can do it.

PC game sales I belive would be at least twice as big or even three times as big if there was no piracy.

X360 software sales is only affected like 15-20% or so id guess.

RRod wouldn't deter people from modding the 360 when its only 200 bux versus an entire library of games. considering its just flashing the DVD drive the risk isn't as high as it once was.

used games on the other directly hurt devlopers by having people who would buy games give all the profit to the retailer rather then a portion to the devlopers.