I'm exhausted and fed up trying to trouble shoot this issue. I have a new post at http://www.facilitiesservicesnet.com/2013/04/18/branding-the-brand-experts-installing-allsteel-beyond-wall-for-canadas-glenn-davis-group/.
Regardless of whether I use the LI share button or paste in the URL at the LI update box, the post image is not being generated.
I created 2 test posts and tried them. Same result: post excerpt is generated, no post image.