The comments at Bertalan’s Facebook post pointed me to Feedheads, a Facebook app to share Google Reader items.
Here’s the problem – I don’t share individual items in Google Reader. Most of my tags are public by default (here’s bioinformatics for example) and if I like a post, I star it (and the starred list is public too). These apps for sharing feeds would be much more useful if they aggregated my starred items and/or all posts under a tag, IMHO.