The options that allows search engine indexing of the tags blog seems to cause the main domain page also to be reset block search engines. This went unnoticed for months - ow! Ever heard of that? How to prevent?
http://wordpress.org/extend/plugins/wordpress-mu-sitewide-tags/
Ok, I think I found my answer. I had it set not allow SE indexing of the "tag" blog posts since they are duplicates of the original posts, and thus might result in Google demerits. At the same time, I had my main site set as my "tags" blog. This apparently tripped the privacy setting for the whole main site. This leads me to another couple of questions. I notice in the plugin settings that it says there are "advantages and disadvantages" re both options, i.e., separate tags blog vs main site as tags blog. I'm guessing this is one of the disadvantages of using the main page as the tags blog? What are the disadvantages/advantages of using a separate tags blog? Could I show the tags blog excerpts on the main blog via Genesis featured widget like I do now? Can I change to a separate tags blog midstream?
Could I show the tags blog excerpts on the main blog via Genesis featured widget like I do now?
It is possible to do that but the SWT plugin does not provide that functionality.
Can I change to a separate tags blog midstream?
Yes. You can change that as often as you like.