[chriswarbo]

Many dynamic things can be accomplished client-side these days. I see no problem with that, as long as it degrades gracefully to some default fallback.

In other cases, it's probably best to have each stateful system as an isolated component. For example, having a dynamic checkout doesn't require the news section to be dynamic. In fact, if you can isolate components like your checkout, you may be able to have someone else manage it for you. For example, at a previous job we used FoxyCart to deal with online checkouts; we just embedded specially-crafted URLs into our pages (although those pages were still running in Drupal!).