Well, in my limited spare time I found a new obsession. Again of questionable use... but I'll be dumping some progress here. Eventually this will become MC Hammer, an alternate Minecraft client.
First steps. Ran Minecraft and dumped the TCP stream via Wireshark. Thanks to #mcc on irc.esper.net and this excellent wiki documenting the protocol, I managed to parse some wireframe geometry out of it!
Some time later. I have texturing working etc, but it's Minecraft-style so not very pretty. I focused on working out the protocol and now render all world geometry. Next up, implementing my ambient occlusion scheme. Here are some first results, showing AO and some basic ambient shadow. The latter is done per block, and you can clearly see the squares. It's going to be blurred and interpolated.
Ambient shadow is filtered and interpolated... starting to look nice now I think. A little bland though. I need a good texture set.