Facebook on Friday dropped a bomb on its user base by launching changes to its homepage, which immediately treats its 300 million users to a real-time “News Feed” interface when they log into the social networking site. The new “News Feed” format, resembling a semi-chaotic chronological Twitter-like interface, features friends’ updates with a “top stories” feel by showcasing what it deems as the most important, entertaining and interesting posts of the day. The News Feed format parallels the original Live Feed homepage interface, on which Facebook users could view a chronological list of their friends’ status updates and postings.

One small misstep in many users’ eyes — Facebook essentially picks what it thinks your top stories are going to be based on a variety of factors, including how many friends have liked and commented on the displayed posts, and how likely it thinks you will be to comment and interact with the Facebook contact. This of course is based on a metric that is not entirely understood by its user base.

Consequently, what is designated an improvement, however, often results in friends’ Facebook posts being accessible one minute and hidden the next, without a discernible reason why. The social networking giant justifies its move by saying that users will basically have the best of both worlds — they’ll be able to have access to the most interesting highlights from days past as well as the most current posts — just perhaps not exactly when they want.

“You will be able to catch up on what you may have missed while you were away from Facebook and then easily switch to the real-time stream when you want to see posts as soon as they’re shared,” said Facebook’s Raylene Yung in a company blog post Friday.