It is SO, SO, SO much safer for them to be rear facing. There are some crash test videos circulating on the net - do a search for them. The difference is just heart stopping. The child who is rear facing barely moves. The one who is forward facing is SO scary. I still have my 16 month old rear facing and I plan on keeping her that way for quite some time, she is still very comfortable.
I have to also add that it has nothing to do with the muscles in their neck - that is a common mistake that people make. It has to do with bone strength. The bones become strong enough at some time around one year, but you can't tell that without a bone scan. I have heard so many people say "Oh his/her neck control is great, so I put them forward facing early" Ugh. Can you tell this is a hot issue for me?! Keep your babies safe! :)