Thanks go to Chris Pendleton for pointing me to this: http://www.bing.com/community/blogs/maps/archive/2009/08/11/publish-your-photosynth-to-facebook.aspx
It's a little more manual than I like (you have to retype a synth title, description, find the link for the thumbnail image, etc.) but it lets you share your synths on Facebook. It's a start!
If we could automate the thumbnail URI and synth description retrieval from the collection ID, that would be much better for me, although retaining the ability to add your own description would also be appreciated. The ability to tag Facebook friends in synths would really drive this app forward.
Also, comments on the synth should link to the location in the synth where the commenter was when commenting like a highlight. Conversation about a synth is context dependent and making people verbally describe which photo they mean is not the way forward.
Regardless, congratulations and thanks to the guys who made MySynths!