With the new twitter limits you can put 16x16 characters with 24 characters to spare. If you use the braille character set, this puts you at 32x64 available pixels. Realizing this, I figured the best use of my saturday was to make tetris. If anyone has any questions, let me know!
Emojis, which get converted to constant width images, seem to be more predictable though. usable max width here is 14 for single tweet view.