Every now and then Steam loses connection and doesn't reconnected afterwards, I've tried waiting for hours at most. The only way to reconnect is to restart the Steam client as far as I know. When the connection drops during a multiplayer game, I'm instantly thrown out. When I have "no connection", I can browse Steam Store and Community pages for some reason, but can't join Steamworks multiplayer games.
This can't be related to Steam maintenance or server outage as I can instantly reconnect by restarting Steam, or wait infinitely for connection.