When a site is redesigned to be more personalized several things change.  Page views, especially for some pages, may go down drastically, due to Ajax and Navigation changes - at least, that's what I've noticed.

Another sticking point - Analytics for a site that personalized is more complicated; if you go all the way with personalization, no two people would see the same page - and recreating the page someone else sees at a certain point in time may be next to impossible to accomplish (with the web tools that exist today - perhaps this will change in a year or two).  And storing all that data - plus aggregating it into usable segments - demands a lot of thought.

But that's the structural and technical aspects of personalization …. what about the behavioral part - is a highly personalized web experience the right way to go?

According to Holly Buchanan at GrokDotCom …. the answer depends on how much control the visitor retains over turning on/off personalized results (and being aware they're happening when you think they're not…IE: transparency).  In Why "Personalization" scares me, Holly mentions why Personalization could be a bad idea:

"…What I'm talking about is, displaying different content for different customers. The customer is no longer in control of what he or she sees.

Do you really have enough insight into what someone is thinking, or what they truly want, from their observable behavior?"

The problem is that no one can predict, for sure, 100% of the time, what a visitor actually wants to see or what they're really searching for; Personalization is based on being able to determine, through various means, what your visitors want to see ahead of time or as they are interacting with your site.

"…Don't get me wrong. One of the most powerful things about the web is the ability to deliver customized experiences. Future Now is all about creating different experiences for different customers or personas. But nobody can't predict with 100% accuracy exactly what every customer wants to see. That's why we create different pathways or scenarios [define], but we let the customer choose which one s/he will take.

Instead of dictating what customers will see, we allow customers to decide which pathway is best.

And it's entirely possible that visitors don't actually know what they want, in some situations.  That's why I think Mike Moran's approach of doing changes in small steps and measuring the result is the right way go with personalization testing….don't over personalize your site and let people easily turn of personalized results when they want to.