I'd like to hear everything related to proper warding, and proper mushroom placement. I've found that sometimes I'm the only person on the team who bothers buying wards. They really do help in some games, even in changing the momentum of the game (I hope in those games my teammates will think to buy wards as well in the future).
Anyway, if I know that the golems / lizards will be visited (either b/c I see junglers on the team or I see our enemy with buffs a lot) I will ward them.
Other times, I want to be able to push a lane for as long as I can b/c it's pivotal to gaining the advantage, yet I don't wanna die like every other lone noob out there. So I'll place a couple wards in places where I think they'll show up.
Warding baron is a no-brainer. It all depends on when I / our team feels like they could baron.
When we're losing out on towers, I like to ward near our jungles so our team can venture out a little without getting jumped. When we're winning on towers, I like to ward their jungle so we limit the space they can roam without getting ganked. Suppose they could go nowhere without being seen by a ward. Then the only safe place would be in their lanes, where the enemy late game champions would be limited to attacking minions.
I've attached a picture of a map with green lines indicating the paths you can take, to make it a little clearer where people are going to travel. The dots are self-explanatory. If you would, save the image on your hard drive and edit it to show where you like to place your wards / shrooms, and explain for what purpose, be it general map control or w/e.
Map control isn't discussed so much on these forums, and I'd like to hear more about it.