Twitter reached 20 billion tweets over the weekend. That’s billion with a “b.” To put things in perspective, Twitter reached the 10 billion milestone less than six months ago. That’s a lot of tweets.

The summer blockbuster tweet came from a user in Japan, demonstrating the global prowess and influence of the microblogging site. All this, despite experiencing some downtime and scheduled maintenance over the weekend.

I’m not even going to begin to discuss the reasons why Twitter may have seen such an enormous leap in activity in the past six months–nothing really surprises me anymore when it comes to the usage stats around social media.

But there is the World Cup. The major sporting event got a lot of attention on Twitter over the summer, helping viewers stay connected and bringing the games full circle to social media and the states.

There’s also the aggressive changes Twitter has made in the past year, pushing out dedicated mobile apps, feature overhauls and an authoritative approach to ads around microblogging. The changes have led to more development around complex apps, while incorporating the features users have been seeking more directly for their Twitter experience.

Last month Twitter announced its plans for a new server farm to handle its growth and activity, while also making the service more social with recommendations for new users to follow.

And as much as I’d love to go on conjecturing about Twitter’s doubled tweet stats, social networking as a whole is getting a lot of love right now. A report released by Nielsen this week shows online users spend nearly 40% of web time on social networks. Sure, Facebook privacy is a thing of the past. But that hasn’t stopped us from visiting the likes of Facebook, Twitter and YouTube.

The report is confirmed by Facebook’s own summer milestones–it’s got 500 million of its own users to fuss over.