I just listened to the latest episode of Rudi and Adam's Beyond Web Analytics podcast, all about data layer standards. This may sound like an esoteric subject but it's going to become really important in the future, and is key to out industry moving to the next level.
As technologies mature, there is always a tendency to standardize so that we can move to the next layer of abstraction. It means we've worked out the details of things that practitioners have embedded in their practices and we can move on to bigger and better things at higher levels.
So what is a data layer? In "traditional" web analytics implementations, you push information to your web analytics platform using its own platform-specific mechanisms. To record a "Newsletter signup" event in Google Analytics you might use:
_gaq.push(['_trackEvent', 'Newsletter', 'Subscribe', 'Customer list']);
in Omniture you might set: