I spent some some writing titles, captions, keywords, and copyright info for my photos in the metadata before uploading them, only to find that the smaller resized versions of the photos do not retain any of this information at all! So it is not surprising that Google has a such a hard time finding anything on this site. Perhaps the metadata should be retained for the smaller versions, eh? After all, these versions are the ones that will available to the public, and therefore out there for search engines to find. I don't know about you guys, but I don't share my original files...
I also use Flickr, and Flickr retains this info for all resized photos, so I think Zenfolio should too.