The latest steam update, released 29.11.07, is causing problems for some users who are using the Steam Friends Overlay. These problems include massive CPU and Network usage for both single and multiplayer games, rendering the games to the point of unplayability. If you are one of these people who are affected by this update, you should turn off the steam friends overlay (settings > in game) and it should fix the problem until valve releases a fix.
More like a reoccurance of an old issue I guess. Some people have only had it happeningsince latest steam update (me included) according to the steam forums.
I didn't know about this. What you mean massive CPU usage and network usage. They just get super laggy or what?
massive CPU & network usage = lots of lag because the Steam Friends overlay is taking processor cycles/bandwidth away from whatever game you may be playing, causing it to slow down.
never had any problems here though (well except for the map loading and steam overlay at once crash )