I would definitely wait until your son is AT LEAST a year old before you turn him around. Really, one year and 20 lbs is the MINIMUM for forward facing, not the "time to turn". The American Academy of Pediatrics recommends that your keep your child rear-facing until the limits of your seat (most convertible car seats rear-face to 30-35 lbs and have higher backs to accommodate taller children). The reason the AAP and pediatricians recommend rear-facing to the limits of your seat is that,rather than a specific height or weight, it's really all about the development of an infant/child's spine, and the weight of his or her head in relation to the rest of their body. When you get into a collision, your head and body tend to move forward (which is what causes whiplash). A small child's spine isn't formed enough to take those forces, and something called "internal decapitation" occurs. Basically it means that the spine is severed from the head. When that child is rear-facing, the back "shell" of the car seat is taking those forces instead of the child's neck, and he or she has less of a chance of being harmed.
Is your son still in the infant ('bucket') seat? It may help to move him into a rear-facing convertible seat. Convertible seats are great because they can be both rear and forward facing (so it's not like you're buying another seat just to last you a month). Also, once an infant reaches about 6 months of age and can hold their head up well, you can also install the car seat more upright (this is easier to do in a convertible than in an infant carrier-type seat). That way older kiddos can see out the windows and not feel that they're laying down.
A great video about rear-facing: http://www.youtube.com/watch?v=Y2DVfqFhseo
This is a picture of my daughter from May. It's not an awesome car seat picture, but you can see how her legs are froggied up a little. She's 27 lbs and about 36 inches tall (mostly leg). She's been forward facing once and HATED it. She didn't have anywhere for her feet to go and kept trying to fold them up indian-style. Obviously, I'm not at all worried about her feet or legs in the event of a crash. Honestly, I'd be more worried about her neck and spine. She is extremely vocal and communicative, and has never once said she was uncomfortable rear-facing. Didn't want to be in the car? Sure, she's complained. I'm not sure if this picture thing works, but here we go: [IMG]http://i55.photobucket.com/albums/g131/tarynsmum/Radian28...
If you'd like more info about car seat safety in general, check out www.car-seat.org. There are lots of certified CPS techs (myself included) and technician-instructors that are extremely knowledgeable and helpful.