I held off thinking it would be a pain as I'm not good with PC's but it is easy. This site works great there are probably others as well:
UT3MOD.COM
Just click on the download and direct it to the USB stick, it is very fast. Pop the USB stick into the PS3. Go to the Unreal III's Community Menu then My Content and then press Square and select the USB stick.
Delete the data on the USB stick then do again. So far it seems you can only do one at a time but it goes very quickly.
You can download off the web from the PS3's browswer as well but then you'd have to quit the game each time for new content as far as I can tell. PC to the PS3 seems much faster as you don't have to quit the game.
FYI, some of the instructions on the websites are outdated saying you need to place the dlc onto a certain folder. That isn't the case anymore. If the USB is the F:/ for example you simple download it directly to that, no folders or anything.
