Depends on the game. If Steam's in offline mode, the recent Aliens vs Predator game can't save your singleplayer progress or connect to LAN multiplayer servers. It is completely dependent on the Steam Cloud and Steamworks matchmaking.

Fileshack has a fast mirror of Daggerfall currently downloading at 200kB/sec+.

Also, Slickdeals broke their servers long before the Slashdot effect took hold ^_^