After building TT Marketpress front end, we wanted to build an advanced theme for Marketpress with all the features Etsy provides.
Unfortunately we never managed to finish it, because we are too busy with other projects.
One thing that we had ready for it was the TT Multisite Like & Follow plugin.
This plugin was meant to mimic Etsy "follow store" and "favourite product" functions.
Today while looking through my old projects I found it, sucessfully tested it with latest wordpress version and decided to give it away for free on wordpress.org.
The plugin's class offers a lot of functions that can be used to improve theme templates and you can find docs for it in a pdf inside the plugin.
Plugin can be downloaded here: http://wordpress.org/plugins/tt-like-follow-for-wp-multisite/
I thought that maybe few wpmudev members were looking for something like this for their etsy style marketplace.
Hope you enjoy it.