Fo those of you who are still unsure of the details of Forge, go download and listen to this weeks Bungie Podcast... your questions will be answered.
I listened to it a couple times this evening, and all I can say is that this is going to be revolutionary for the game, even more than any of the other features that have been discussed.
Imagine setting up maps and gametypes and being able to save them and upload them to the Bungie servers so that anybody can DL them and try them out... Bungie is even going to feature fan-created favorites.
The possibilities are endless for customization. You can close doorways with objects, drop teleporters to create new doorways.. you can even drop teleporters on people!
Yes you can shoot monitors, they have a stardard shield just like a player, difference is that you wield god-like powers.
This is for unranked, multiplayer only games.
Go listen to the podcast.