I just want to jump-in and provide a little clarity to the information Charles provided (which is mostly accurate, but not 100%). BTW - my company is a Google Analytics Premium Authorized Reseller, so we work with this product on a daily basis.
GA (Standard & Premium) is pretty strict when it comes to privacy, so there are fewer opportunities to track individual users because of that stance. However, the GA Premium TOS does allow for more flexibility in this area, allowing you to track unique but non-identifiable information like visitor IDs or member IDs. In general though, if tracking individual user behavior is critically important to you, Omniture does offer more in this area. (Keep in mind, Google has to be more sensitive than Adobe when it comes to privacy because of their reputation and scope of business.)
Second, GA (Standard & Premium) does allow you to create on-the-fly segments and apply those retroactively. The Advanced Segmentation feature of GA is probably the most powerful feature of the entire system, and in my opinion much better than anything you can find in a competing solution.
As for the price, GA Premium is a flat $150k annual fee. Charles says that "depending on the number of server calls you have...Omniture will be cheaper". Well, the opposite is also true, of course! In my experience, many of the Omniture customers that we have spoken with who are interested in GA Premium are actually paying more for Omniture. It does depend on your traffic volume, but GA Premium doesn't penalize you for getting more traffic to your site.
Let me know if anyone has other questions about GA Premium, I'm happy to answer.
Tyson Kirksey
Vertical Nerve, Inc.
