I never realized that Bitcoins were infinitely divisible . . .
At the moment with the current protocol, they aren't. They are currently only divisible to 8 decimal places, with 0.00000001 BTC being the smallest possible nit that can be transferred between bitcoin addresses. In the future, if it became necessary, a protocol change could occur. Depending on how it is implemented, doing so might require a fork in the blockchain, but if it was necessary there would likely be enough support and acceptance to accomplish it.