Gavin Andresen has changed the Bitcoin code to block any output with a value of less than 54uBTC:
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So, what happens when Bitcoin takes over the world economy, and 54 uBTC is worth a lot of money ($54 say)? Then Bitcoin will only be usable for large-value transactions... It will be more like the existing inter-bank wire-transfer system at that point...
I think a change to accept lower volumes again would be easy to get accepted by everyone.