I need to look further, but so far it appears to me that when one chooses in a browser to view the certificate chain of a secure page, where that secure page references secure content from/using third party domains/certificates, only the certificate chain of the top level page is displayed. The other certificate chains involved are essentially hidden unless one views the page source or runs a traffic sniffer. Is that correct?
If so, I'd prefer an option to see all the certificate chains involved in loading a page's content. Maybe most users won't care, but some will, and it would keep those details from remaining hidden or difficult/time consuming to access.
Somewhat related to this, I continue to be somewhat frustrated at the amount of dialog navigation that is required to view certificate chains in some browsers (e.g. Firefox 3 made the chain viewing dialog deeper nested within a hierarchy of dialog navigation).
My perspective is that, even when users don't fully understand an item, they are good at noticing changes -- we're wired to do so. If the chain is easily accessed, and users are taught to give it a glance, they are likely to notice if/when it changes, particularly for regularly visited sites. They may not know exactly what is going on, but it would likely be enough to inject caution and a google (twitter, whatever) for answers.