Seems like everywhere you look these days, users are given an opportunity to share something via Facebook, Twitter, Google+, LinkedIn, Digg, StumbleUpon, and the list goes on an on. While it may be a bit overboard to offer sharing via so many different channels, offering sharing across Facebook and Twitter can be quite beneficial to a product.
One area where sharing would be a logical fit would be across content sites such as espn.com. On their mobile site, they have a video module that typically had 3 videos that can be selected to be viewed.
After clicking through, you are usually shown an ad and then the video.
When the video concludes, you are taken to a video center page that shows you what video you just watched and asks you if you want to watch any more videos.
At this point, this would be a GREAT opportunity for ESPN to offer the user the ability to share the video via Facebook or Twitter. This is no different than ESPN asking users to share articles via social channels. Except such a medium (video) may even have a more effective conversion rate of bringing new users back to the site.