Since writing my rant about the schema conspiracy of web analytics platforms, I've been giving the whole idea of hit-level data collection a lot of thought. Sessionization is very heavily implemented in Google Analytics, which is understandable, but the regular Google Analytics API just doesn't give you the kind of information you'd need, if you wanted to stitch hits together differently in your own backend. In fact, there are four distinct levels of aggregation that are not exposed via the API, even though I think they should:
The User ID is definitely one of the coolest things about Universal Analytics, if used correctly. It might reveal some surprising insights about your visitors, since now you're not restricted to analysing visitors as just browser or device instances as before, but rather you can build your stories around all the touch points the user might have had on their journey to and through your web properties. With this simple tip, you can extend User ID tracking to return users without them needing to authenticate.