S.,
I just wanted to say Thanks for your post. My son will be three in Dec and we are dealing with the same issue. He goes to sleep in his bed at night but always comes to get in bed with us.
We also have a 6 month old son as well and figured he was getting in the bed with us because he saw his little brother sleeping in our room, next to our bed. The baby has since moved to his own room and won't sleep with us at night.
Again, Thanks for the post, I have learned a lot from the advice you have been given. I am going to try some of the advice given to you so that my husband and I can snuggle all night without a 2 1/2 year old in our bed.