Is the may15 code for first time buyers only?
Yes it's for first timer only. BCB is bing cashback - it is 10% for diapers.com. Quite a few sites are running 20% off right now that you can have diapers.com pricematch to.
I had posted the strollers.com one on another thread - I have to double check but I think it's CARSEAT20. babycatalog has discounts also, you just put the carseat in your cart.
HTH!