Facebook tries to make "liking" the most common activity on the web. What users don't always realize is that there are three distinct likes:
- liking a facebook page. This used to be "Become a fan". It is equal to following the posts shared on that page. Liking a page remains in a list on your profile, so it's permanent.
- liking a web page - this is the "like" button site authors put on their pages. When you like a web page, it goes to your timeline and the news feeds of your friends. It's also permanent, since it remains on the timeline, though a bit harder to find.
- liking a status update - this is the most common action. You express your positive attitude for a status, link, video, photo or coment posted by a friend. But these likes are extremely volatile - they are not stored anywhere in a user's profile. When someone opens a timeline, they don't see "John liked the photo of Jane". The user wall used to contain aggregates of likes, but the timeline abolished that.
The problem here is that it goes against the idea of unifying liking as the action to perform. Do I simply like this, or do I want others to see that I like it? Should I "Share" it? Will my like matter when stories are displayed on others' news feeds? Do I want it to be a permanent part of my profile, or I just want the author to know that I like it. What do I do - "like + share" or just "like". A third option ("share" only) is less likely - if I'd share something, I most certainly like it.
The volatility of a "like" isn't a bad thing - it is an action that you deliberately don't want to be part of your profile. The problem is if users don't understand the subtle difference. In my opionion the best way to represent this is through a single "like" button, that can optionally share the post on your timeline as well. And it makes sense - why liking a page on some site appears on my timeline, but liking a link to the same page on facebook doesn't? Why should you press two buttons when you "publicly like" a video?
How to achieve that in terms of UX and usability? That's the hard question.
*I've tackled the issue of "like" unification in my social network tool, not only for facebook, but as a way to cross-post between social networks, and so far it has been useful, although a bit confusing initially.