Customization is derived through explicit, stated preferences, while personalization is driven by both the explicit and implied – behavioral, demographic and brand specific information. How did the user get to the site (referral information like URL or search keywords), prior purchases, and onsite activity are key to driving relevance on a website.
Consider this, your brands’ website probably constitutes less than 0.5% of a visitors life experience, if you’re wildly successful… there’s a world of insight necessary and available to the purview of your personalization scenario. A world that requires integration with a more comprehensive data set: your marketing database, third party data and analytic models to decipher it.
Visitor Centric Marketing 
Love the short, understandable explanations and your writing style.I was using the two terms, “customization” and “personalization” interchangeably, but now I see the obvious distinction. I’m a new Twitter follower too; I like what I see. Thanks.