I've often wondered about the efficacy of having a simple catch-all script that just tracks everything a user does on the site. I would think it would pound the database relentlessly under even modest load.
One trick is to not use a database but a flat text file. You can optimize for querying nightly.
AWS comes into its own for these kinds of use cases - make a lightweight autoscaling events API on Elastic Beanstalk pumping events into DynamoDB coupled with a bunch of workers running at the EC2 spot price sorting and processing these into a traditional RDBMS = massively horizontally scalable events handling for pennies an hour.
You could read all the responses into a Queue-type structure and then populate the database in the background.
Clickish can do this with GA is you wanted. It's also intelligent with how it routes request back to GA. http://www.clickish.org