I have a Makita 14.4 model 6228. It's great for screwdriving or light drilling at a superlite 3.7 pounds. Only 200 lbs. of torque though. So, I just picked up the Makita 6935 impact driver, which is only 3.7 lbs. too, but has a torque rating of 1200!! They say you can use impact drivers as drills, too, but with less precision. I haven't tried it as a drill yet. However, to drive screws, it's stunning and won't twist on you at all.
Also have two Ryobi 18 volt drills, the P200 and new P201 that just came out. They call the new one "torque power" but it has less torque, 330 inch pounds, although a faster drilling speed, 1600 versus 1300 on the old one. The old one had 400 inch pounds of torque but not quite as nice a balance as the new one. One handed chuck is a nice feature on the new one though, as is quick switch from drill to driver mode. These are both 5.3 lbs. with battery.
Like most people, I'm looking for power and speed, but light weight. Among contractors, there seems to be a trend back to 14.4 volt tools, or the 15.6 volt Panasonics, to deal with weight issues. That's what's so incredible about the impact drivers. Light and powerful!!! Anyone using an impact driver for everything??