My major contribution to this release is the payment module system. The idea is to allow for flexible development of payment modules for most any style of payment backend. I converted the existing PayPal and Authorize.net modules to use the system, and I’m working on a Google checkout module as well. Also, I hope to finish the Gift Certificate module before 0.5, but that may need to wait until 0.6.
I also wrote a nice little interface module, allowing the system to manage subscriptions to a store newsletter using a Gnu Mailman backend. I think that is the best of both worlds, an excellent store, leveraging a heavily tested and feature-full mailing list manager.
On a personal note, being a core developer of an e-commerce engine is a good business move. I’ve already gotten three gigs simply by my association with the project. Nice. It certainly spurs me to remain active with the project!