How cool would it be if you could look at your servers behind a VIP on a load-balancer and tell which servers were serving more errors, serving traffic slower, or not getting the requests they should be in comparisons to your other servers. I have a product in place to do just this, its not released so I can't talk too much about it.
The issue is that we have to embed some of the data in the http requests, or cookies, which I need help from development to do. I am getting pushback about security, and information disclosure which I am fighting through. I understand it could be an issue, but it's the only way that we can properly track usage and performance. This would rally help a lot to have as a internet based standard for tracking requests and backend connections and usage. Using weblogs is not feasible when you have thousands of servers that don't have any consistency. This is my first pass at what I want to add to the http headers:
Unique ID of request
Something like fcweb01 + last 3 from ip range (.124) fcweb01124