Actually I think i remember Satoshi or Gavin saying that it actually is a quite easy change as bitcoin was designed so that decimal places can be added indefinately.
Wasn't me. I don't remember Satoshi ever writing something like that, but I'm really good at forgetting things.I agree with ribuck, if we ever need more than 21quadrillion bit-atoms, encoding more using the unused high bits in the 64-bit number will work nicely.
That would be a very nice problem to have.