Bloomberg published an article on synchronizing the exchange clocks. Not a big deal you might think but then you're wrong. A lot of infrastructure is worthless without having an accurate idea of when something was traded.
ESMA is taking this a step further: they want to see nanosecond accuracy on time stamps. You can read the article here.
EDIT: Interesting post from some professionals on time recording. What the ESMA is looking for, is extremely difficult to deliver outside of a lab setting. Read their blog post here