3 months old today!  And with our super-scientific home weight-measuring system (holding him on the scale), he's measuring about 16 lbs (between percentile 75 - 90)....he is a hefty one to carry in the car seat!  Here are the comparison stats:

1 month old
11 lbs

3 months old
16 lbs

Current developmental milestones --

Smiles a lot! 
Coos and "talks" all the time. 
Can sit up in the high chair, bumbo, and other places when supported. 
Holds his head up easily. 
Smiles at us when we first see him.
Can hold his head up well when laying on his stomach.
Grasps at his hands and other objects -- and he's getting better aim every day!
He's laughed a couple of times, but hasn't yet done it consistently.