I was in three different games this past weekend: a Dr. Who RPG using D20 Modern, a Warhammer Fantasy Battles game, and my Warhammer RPG. They were a little different from your average series of games. The two RPG sessions were fairly short (about three hours), and the fantasy battles game went fairly quickly (about an hour of play time, I think, after around an hour of set-up). Each one had alot packed into the time, though.
The Dr. Who game is on a Friday night, and I think we started playing around 8:30 and ended around 11:30. There was alot of story and investigation stuffed into the time. The players took the time to unravel the mystery in the story, as well as soak up the atmosphere. By the end of the story, the group was going through a fortress inspired by one of the original episodes of the series...The Daleks.
The Fantasy Battles game was a great introduction to the hobby. My three units of Bretonnian calvary (with a little help from a few units of archers) carried the day against an army of Lizardmen. There was maybe an hour's worth of playtime, but it was great fun, and inspired me to really built a bigger army. We talked a little about how to augment units with different models, which helped me re-imagine how to design different units of men-at-arms and archers.
The Warhammer RPG Sunday had to be shortened, since one of the players had to leave early. The PC's started their trek to the Imperial capital of Altdorf, following a pack of mercenaries. There was some strong character building (with one player changing his career due to interactions in the adventure). There was one encounter with a pack of undead soldiers, and the survivors moved on.
Each gaming session was considerably shorter than what I'm used to. Everyone put alot into each session, though.