My hubby and I bought the Graco Infant Safeseat for babies up to 32 pounds. First off, the carseat weight 9 lbs, and my son was over 9 lbs at birth. So right off the bat, I was toting around almost 20 lbs. He quickly gained weight, and now at 14 months, he weighs 28 lbs. Needless to say, when he was about 5 months old, we started leaving the seat in the base in the car, and just took him out and carried him, which presented a problem because he could not yet sit unsupported in grocery carts. In my opinion, I think the concept was great, but in my experience, it just turned out to be a real pain in the butt. The other thing to consider is the fact that the seat tends to be a bit longer, so putting it directly behind the driver's side causes the driver to have to pull their seat way up, which is ok if you don't mind your knees being right on the dashboard:) Overall, I think that it is more trouble than it's worth.
K.