You can use the case as the motherboard now if you dont mind single layer setups, they put a copper layer on the case and etch off the bits they dont want, and it can follow curves and everything. No good for a motherboard yet though.
You can also get flexiable sheets that are circuitboards, kind of like the ribbon that connects the A1200's keyboard to the motherboard but with chips on them.
the big thing though is to make cheap computers, and cheap computers mean standard technology, so you wont be seeing any super special boards unless a very good use comes around.
As for just designing a circuitboard into a circle or something, yeah thats easy but the little extra space you have gained isnt normally worth the trouble so a smaller square one is used anyway.
