Hi Jeff,
We built out a subscription center about a year ago - http://www.visioncritical.com/subscribe
We had some challenges, I wanted to build the center with segmentation, snippets and dynamic content. The issue we ran into is that you can have a lead be a member of only one segmentation, so we had to run every combination of subscription channels as it's own segmentation which means we cannot add any additional channels to the center.
We will likely be re-visiting this and re-building it in the future so I'm keen to see what other examples get posted.