First of all, we LOVED having an Amazon registry!! It seems like not everyone is comfortable using an online registry, which is a shame because it's so easy, but as someone who registered through Amazon I would give it two thumbs up. They make it super simple and provide a thank-you list with addresses. Awesome!
Second of all, my generous brother-in-law allowed us to order some of the remaining items on our registry using his Amazon prime account. Why yes, I'd love free 2-day shipping, thank you very much.
Third of all, I wish we hadn't done a Target registry. It doesn't always record things that have been purchased, Target's shipping isn't consistent (and by that I mean it's pretty slow!), and the things we chose often showed up as different when viewed online.
One note: even though it's totally awesome to have the ability to register for things elsewhere, the purchasing isn't straight-forward and seemed to intimidate even the tech-savvy gift buyers. I was disappointed by how few things were redeemed at the bottom of our registry.... stuff that was sold by IKEA, Etsy, etc. I don't know if Amazon has the ability to make that process a bit more streamlined, but if so, they totally should!
We have been really blessed by the generosity of our friends and family. Our little one is so well cared for and has received so so many great gifts. Plus, way to go, Amazon- your registry rocks!