The other day I ordered a pizza for 16 mBTC.

Doesn't that sound more natural to you than 0.016 bitcoins? The name "bitcoin", by invoking the noun "coin", just naturally suggests to people that it is an indivisible unit of currency. I could offer you "half a coin" of US currency, and although that's theoretically possible (I could saw the coin in half), it just doesn't really make sense when we consider what's traditionally understood by "coin".

Really, the ideal compromise would be to rename Bitcoin to "Bitgold" or similar - something that doesn't carry connotations of a whole unit by which trade is carried out - but obviously, at this point, that's almost too ridiculous to even consider. "Bitcoin" is here to stay, but if we're going to make people realise that they aren't limited to paying discrete multiples of one bitcoin, then the transition to mBTC as the principal unit of bitcoins is a good way of achieving that. It's also built into the concept of the infinitely divisible currency that we can continue to do this forever.

If and when a satoshi comes close to parity with the dollar, I'll be an advocate of switching to satoshis - and for some reason, I don't think that transition will be taken as poorly as this one has been. For some reason, people just seem uncomfortable with the term "mBTC".

P.S. the pizza thing is true, it was delicious