Get an infant carseat or just go right to a convertible car seat?

I already have our convertible seat and am really debating the infant car seat. The only reason I had one for my son was because the carseat was given to us brand new, but we really didn't keep him in it for longer than about 2 months as I hated lugging that thing around. We moved him into the convertible car seat, and then I just wore him everywhere I went after that. It seems silly to spend $100 on a seat that we will only use for a couple months when the convertible can accommodate babies as small as 4lbs.

Is anyone just doing the convertible car seat?