DH and I just completed our Buy Buy Baby registry yesterday and I thought I'd share some things we learned in case it helps anyone.
1 - You don't have to wait for your completion coupon to come in the mail. You can go to the store and tell the reg counter you're ready to complete, and they will print you a coupon in store (they will void the one in the mail so no extra!).
2 - You can use Bed Bath and Beyond 20% coupons but not on furniture, we used it for our crib mattress which IS eligible and saved $60.
3 - Any other Buy Buy Baby coupons have to be on a separate transaction, so if you have one for more than 10% that you want to use, be sure to split it out.
4 - If you special order or back order anything, they can't ring it up under the coupon separately from everything else, so be sure to have the salesperson that writes up the order for you take the discount off when they write the invoice.
The process took a LONG time (around 2 hours - we had to get furniture and a few other large items) but the sales staff was very helpful.
GL and HTH!