Getting NOLed: Some players have the ability to transform your character into Nol, from one of the offline missions. To avoid this, use only LOCKED games with people you know.
Peaked Items: If someone offers you an item with +99 on theend, DO NOT ACCEPT IT! This is an illegal weapon and not only does it ruin the game, SEGA disconnects people from online who has them in their possession.
You need another controller plugged into either slot 2, 3 or 4. Using that controller, hold down the L and R triggers and press 'Up' on the directional pad. You will then see the view of one the other online players. Very helpful if you don't know where they are!