Thanks, on the BigIP cookie. I was hoping it might be a unique id, bt alas not.
What we're doing is creating a unique visitor ID across all our clusters that is used in our applications. We have several clusters and no common, unique id that can be shared to correlate across products. To solve it in the applications can be error prone from a development perspective, and we want to drop a unique visitor cookie at the load balancer. Most of the products go through the load balancer, so it's a good place to do it.
Right now I'm moving forward with implementing portions of the tcllib UUID to get as unique as I can identifier. My main concern now is performance and load on the LB.