Varys from game to game. Some game demos files are alot bigger. It also depends on what your doing. If you just leave your PS3 on your XMB, it'll download faster. If your playing a game or demo, it takes a little longer to download.
Call of Duty: World at War, Socom Confrontation, Resistance 2, Metal Gear Solid 4: Guns of The Patriot, Grand Theft Auto IV, Ratchet and Clank Future: ToD, Call of Duty 4, Warhawk, Resistance: Fall of Man, Rainbow Six Vegas 2