Scientific American posted an overview about tectonic plate movement, datums and geodesy. The article covers a fair amount of ground in some depth, but not so much so that it's confusing. Check it out and contemplate the amount of work that we'll all be doing when the USGS updates the datum in another few years.
For those who are curious, Cartographica maintains a large list of datum and datum shift information so that it can accurately overlay coordinates from one system onto another. These calculations aren't trivial and we had quite a time squeezing these conversions into the first version of CartoMobile within the space and processor constraints. However, it all paid off as the iOS ecosystem has gotten stronger and we've been able to maintain accuracy between the iOS and OS X versions.