Social media moves so fast, it's hard to keep up. Here are the week's top stories in scan-friendly format:

  • Why Fridays Mean Engaged Social Media Participants
  • StumbleUpon Hits 1 Billion Stumbles
  • Twitter Local Trends Adds 70 New Cities
  • Extragram Gives Instagram Photos A Web Presence

Why Fridays Mean Engaged Social Media Participants

Buddy Media, a social media firm, recently found that engagement peaks on Facebook on Thursdays and Fridays by rising 18% when compared to the rest of the week. Twitter executive Adam Bain also said Twitter users are more engaged on Fridays. But the question remains -- why?

Mashable recently dug into this question and revealed that, as you might guess, as workers minds start to wander to the other matters on Fridays, they are mentally checked out and look to services such as Facebook and Twitter for distraction. Also, there are fewer posts on Fridays, meaning audiences on social sites click through more on average as the week drags into Friday.

What about you -- do you check out social media more on Fridays? Are you looking into your social circle on these networks and are more apt to click on fun ads or interesting stories as you seek distraction?

StumbleUpon Hits 1 Billion Stumbles

We talk a lot about new social media sites such as Facebook, Twitter and even Digg now and then, but there are older sites that keep chugging along, powering the social web in their own way. StumbleUpon is a fine example of this, as the recommendation engine is now hitting 1 billion stumbles per month. This means that 1 billion stories are flipped through on the service every 30 days.

This is a huge growth number and means that, in the last month, the monthly stumble count has grown by 200 million, when the company last published the number. Users of StumbleUpon obviously get hitting the Stumble button to go to the next selected site, which is selected for you by the service because of preferences indicated by your profile. Also, the service has a thumbs-up and -down button that allows on-the-spot machine learning from your tastes.

Are you a StumbleUpon user? Is it a good way to find fun sites and web pages that you enjoy? We hope to see some great discussion in the comment section below.

Twitter Local Trends Adds 70 Cities

One of the more interesting aspects to Twitter is what is being said. More important, what are folks talking about in your specific city or location? Twitter Local Trends gives you a window into trending topics based on your geography. This week, Twitter announced an upgrade to this service that will make new Twitter-ers happy.

As of Monday, Twitter added local trends to 70 cities, meaning the grand total is now over 100 locations around the world. To check out the new cities and the respective trending topics there, hit "Change" in the Trends sidebar on Twitter.com and now you can see trends from places such as Santiago, Jakarta, Kuala Lampur and many more.

This is a nice development from Twitter and will help the service overcome the image of it being a US-focused technology and more a citizen of the world. Of course, adding more languages to the site and more SMS local numbers would help too, but Twitter is obviously looking to grow its international audience with trends in these new locales.

Extragram Gives Instagram Photos a Web Presence

There's a new trend happening in mobile: Photo sharing. Yes we've been emailing photos around for years, but services such as Instagram and PicPlz allow us to take a photo, apply fun filters on it and upload the image to Facebook, Twitter and other social sites around the web.

A complaint of Instagram is that photos taken by the service are only available through the app. Now Extragram gives a web site for folks to see Instagram photos. Extragram complements Instagram by providing a web-based view into the photos taken with the iOS application.

Using Extragram, you can find photos based on places, people and hashtags. When you roll over a photos with your mouse, you can see comments, add a "like" and interact with the photo in a more detailed manner.