I have a Chicco Keyfit 30 from DD that I will reuse with DS. It fit fine in my Altima.
My DH is tall (6'2"), so it had to be installed behind the passenger seat in the event that he drove my car. I am 5'2", and could have easily installed it anywhere in the back seat. It made for an uncomfortable ride as a passenger though, because we had to move the passenger seat up quite a bit.
We stopped using the infant carrier when DD was about 11 months old. She was still technically well within the limits to ride in the carseat safely (about 20lbs), but it was just getting too heavy to lug around. DD was obviously much more alert/awake by this time, and enjoyed sitting in a grocery cart, stroller, etc...so keeping her in an infant seat wasn't necessarily practical anymore.
If I had to do it all over again, I think that I would have went with a smaller infant seat - either the Chicco Keyfit or Graco Snugride that only goes to 22lbs.
(And in case you're curious, we went with a Britax Marathon when we switched her to a convertible. She's still rear-facing. It takes up less front-back space than the Chicco KeyFit 30....so the passenger seat has a bit more room now.)