Try not to get over anxious. It is good that you are aware, but the chances are there is nothing to worry about in your case. As long as he is making his milestones, is talking and crawling/walking and begins to interact socially then all is okay. But you are going to have to wait to see if those things develop. As crawling is associated with brain development you could buy some of those fabric tubes for him to use when he is a bit older. Just enjoy your children and stop worrying!!! At the end of the day if your child is/isn't on the spectrum there is nothing you can do about it and worrying makes no difference to the situation apart from making you ill.
Does make eye contact but sometimes I feel like he is looking past me and not actually at me. He does smile at me when I smile at him. He has just started to giggle when I play the "Im gonna get you" game. He LOVES his older brother and giggles until he is out of breath when they play. He goo's and is starting to baby talk. He likes to be held for the most part. Sometimes when he is over tired or doesn't want to be held he arches his back and gets mad. He can push himself up on his hands while on his tummy but cannot sit alone...still a tad early for that though. He likes to be held when he sleeps and likes to sleep next to us. If we put him in his crib he very rarley sleeps through the night. He will be 5 months on 11-7-08. I ask because every where you go you hear autism...autism...autism...and how it is on the rise and how it's more common in boys and on and on and on! It really freaks a mom out! I had issue with my 2 1/2 year old, he would flap his hand and walk on his tip toes..all of which he has stopped now but those are red flags...but for him it didn't mean anything. He is talking up a storm and is definalty not autistic. I guess sometimes the more you know isn't always a good thing.
It is very early, but you would still be looking for eye contact, gurgling, reaching out, how does the baby react to being held by you and other people. You would also want to keep an eye on motor development such as sitting, especially crawling etc.
But why the question?