I need to investigate the Wallet API (and whether the Play Store is using it) but I'm pretty sure it was the Google Wallet checkout popup that actually kicked the bucket. The Play Store site was really snappy, actually.

The order that visibly went through was redirected to the full Wallet site. I say "visibly" cause apparently one of the popup ones went through as well. Oh, well, I'm sure one of my friends would appreciate it.