When my current group got started we'd meet once every two weeks, and game between 8 and 12 hrs a session. Here are a couple of secrets that I've noticed that keeps our games interesting, and going:
1) Eat. Stop and eat. Whether it is the ordering of the pizza, and hitting on the delivery girl, or if it is actually sitting together and making the food. (Done both, different groups, but still.) This get's everyone's mind off the game for a 1/2hr or so.
2) Cigarrette breaks. We are smokers, so after about 2 hours, it's that time. So we break for a good 5-10 minutes and step away from the table. The non-gamers in the group play x-box or ps2 or watch some tv.
3) Mix up the game. We play two games a week, so this isn't so much of a problem with us. But when we were just playing one campaign a week we got the boredom everyone talks about.
4) Invite people to watch. Some people don't like this, but it helps to kepe you going when someone is watching you. We usually have one or two gf's over during a session. Besides, it makes them feel involved.
5) Ban magazines and non-required books. When the game slows the players grab their other books, and it degenerates from there.
6) Sit at a table. I know this sounds wierd, but actually play at a table. And don't have couches where people can stretch out. This is the killer. Our games got more interesting, and had less petering out after we moved to a table every week.
Just a couple of thoughts.