For over a year now, the Like button enables you to add a comment, and it shares the story on Facebook with the thumbnail and all. Although the share dialog gives more options to the user - they are probably redundant and the extra dialog must have it's drop-off.
The big advantage of a 'share' button is that I can design it as a prominent button.
My question is - are there any studies that show if users click a 'share' button more then 'like' in some cases?