Google reader shared feeds now inherit the tag of the folder(s) they are assigned to in Google Reader. You can see them in the post footer when you view a post within Reader, and if you click on them you get a filtered version of the shared post list:
shows only posts from my "SciTech" tagged feeds, or posts to which that tag has been manually added during Sharing.
The above link requires a Google reader account. For heck of it I tried:
but today that gives "permission denied". Likewise I wasn't able to discover a feed for this stream; the feed associated with the filtered page is the general shared item feed.
Still, it's progress. Soon I might be able to share my sci and tech posts without sharing my (very Dem) political posts.