If you're unsure how to do so. You can do so directly from the game by going into cinema and using the 'record' button to record a short clip. You can again, in the cinema menu select this and hit 'render as video' or something like that.

After that's complete. Hit Export to XMB (not export to youtube as this is poor quality) then exit the game and go to your XMB. Now open the 'video uploader and editor' in the video menu, select the file you just exported to the XMB, and hit next till your prompted for a user and password for youtube. It's pretty simple.

Thanks Joe for the examples! Any new uploads?

I'm writing a guide thing for UC3 so I've been making some demonstrative videos. Select HD or it looks awful.

20 Kill Streak Rampant Medal !!!

Here's one I never posted.