Joscelin, Facebook is simply chopping off the end of the Share Link, meaning that you have an incomplete set of camera coordinates when someone clicks the link in Facebook... + because of this you end up being loaded into a strange place in the synth/pano... or at least looking in an odd direction.
I am assuming that you know that if you want to link to the beginning of a synth or a pano, you just get the link to the view page from your profile + post that (which is short enough for Facebook to leave unmolested).
If you're intentionally using Share Links for their intended purpose of linking to a specific location + camera orientation + zoom level, then (for Facebook anyway + any other website which arbitrarily truncates long URLs) you'll need to use a third party URL shortener such as http://bit.ly
I'm not saying that I think that the responsibility *should* fall to us. I'm only saying that it does.
Don't expect the Blue wave of updates to impact Photosynth.