Valve have made some changes, but they might only be noticeable on the BETA Steam client. We suggest anyone suffering with eggregious ping since 3.4 should try out the new settings on the BETA client.
Steam :: Steam Client Beta :: Steam Client Beta - December 9th
The new client setting is in the “In-Game” section, at the bottom under “Steam Networking”.
Here’s the associated FAQ:Steam Support :: Peer-to-Peer Networking and Sharing Your IP Address
NEW INFO:
All players in the lobby must enable this for it to be effective.