Facebook has removed the blue Comment button from beside the comment box on its website. This appears to affect all Facebook objects that can be commented on: a story on the News Feed, a friend's status, a photo, and so on.
Previously, to comment on a Facebook object, users would type out their post and then click on the Comment button in the bottom right. Now, users are expected to type out their post and hit the Enter key.
This is a very minor change but given how often commenting is done on the social network, it's something quite noticeable. It is one of those things that users will attack with the "don't fix what ain't broke" argument.
Facebook clearly found that a large majority of comments were short and new users were hitting Enter with the expectation that the comment would be posted. The Comment button was always visible, so users quickly realized what they had to do. With this change though, it may be slightly harder to figure out to hit the Enter key to post a comment, but I'm sure users will figure this one out as well (in some cases, Facebook will show a "Press Enter to post your comment" message).
The one problem that I can see with this new method is regarding comments that are more than one paragraph. Users will hit Enter to go to the next line and realize their comment has been posted. They will then have to delete their comment and start again. Furthermore, it will be significantly harder for them to figure out that they need to hit Shift+Enter to create a new line without posting the comment (though again, in some cases Facebook will display a "Press Shift+Enter to a start a new line" message).