Just wanted to let you know about the latest news regarding the Market theme. Due to some requests, I am working towards integrating Authorize.net with the Market theme. Essentially, it would be another bit of code that could be added to the single.php files to allow checkout with both Paypal and Authorize. (Rather than have it included from the start because not everyone would want to use Authorize.) Hopefully down the line a little bit the entire theme would revolve around a Options panel which would allow you to set all the possible payment types (Paypal, Google Checkout, Authorize, etc) and add all the right code - but that is still to come.
So as for when you can expect the Authorize integration to be completed, I'm currently waiting on them to approve my developer account so I can test the code I've been working with so far. Should be a few days and hopefully I'll have it completed. Stay tuned.