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This blog post fascinates me.
Here's a guy who doesn't want to bother calculating the tip on his restaurant check, even though he probably has a palm pilot or laptop or cell phone out during dinner (judging by the importance of wifi access) and could easily use the calculator in said device.
So he rounds everything to even dollars, only to realize that he could be using those precious cents digits to communicate a wealth of information to himself about each meal. Simple addition, subtraction, and multiplication are too much to bother with, but binary/decimal conversions are de rigeur, apparently.
No less remarkable is his discovery that restaurants seem to be pretty lax about the total you write on your receipt.