In the last log I'd completed a 12 x 6 display and had that running. I've now completed 12 x 12 pixels in exactly the same way, although things became quicker and neater the more I did.

Before the reveal I'll note some of the things that I've learned.

1. I've spent a lot of time wiring these little pixels up instead of simply using strips or designing some kind of pcb. Strips were out because I need to match the pitch of the ice cube trays, which are excellent for this job. I also wanted to do this 'on the cheap' and I had a bunch of the little individual pixels. However, I'm sick of the fiddly stripping, tinning, soldering and if I extend this display beyond 12x12 I might try an easier method.
2. I've used RGB pixels. I now know that RGBW would be a better choice because they'd be more efficient and give a better white. (More efficient because for less saturated colours and white, the white LED is doing the work of three. The update time is longer, but that's not really a concern here, I'm not showing video.)
3. I like my modular construction but stitching to a fabric isn't ideal. It has its plusses but even with a non-elastic fabric, things that were accurately aligned when laid flat have stretched and moved a bit when hung. My improvised foamboard (paper-covered card) is perfect for the job, very light and easy to work with. If they could be joined in some way, they don't need the fabric backing. 
4. I probably need to consider heat dissipation and power distribution.

The point of this is that I can run any game / demo / utility I care to code. Programming is the part that I enjoy the most, so I'll be able to enjoy working on all sorts of ideas. The plasma demo above is one. The music visualiser below is another that I've been working on. (The reason it's currently showing a lot in the bass is because the little mic is between the speakers, if you put your head there, it sounds very boomy.)