I've created a JEvents extension that consists of a component and two plugins and integrates JEvents, usermeta and Google Checkout. I've refactored most of the code into the plugin architecture, but I still need to switch from the Google HTML API to the XML API before I release it (security issues). It has taken me a lot longer than I anticipated because it has been a low priority, but I hope to publish it soon. I guess I'll put it up on the Joomla GForge site when it's done and link from this post.
I noticed you are a "silver member", though, so can't you use Geraint's registration feature, in the meantime?