Is Facebook Finally Slowing Down?

Can it be? Is the world's largest social-networking site finally maturing?

Registration growth appears to be decelerating at Facebook. Founder and CEO Mark Zuckerberg has been trigger-happy over the past year and change in announcing every time that his sticky site has landed another 50 million users. He's been slow in trumpeting the 350-million mark.

Let's go over the date of Zuckerberg's previously announced milestones.

Source: blog.facebook.com.

After a 4-1/2 month gap between the 100 million and 150 million announcements, Zuckerberg's milestone missives were roughly three months apart for the 200 million and 250 million declarations. Forever the speedster, Facebook thrilled fans by hitting the 300 million mark in exactly two months.

Well? We're now more than two months removed from Zuckerberg's last post and there's no 350 million user merit badge.

This is surprising because we're not just talking about incremental milestones. Every 50 million aggregate users represents a smaller gain on a percentage basis. For example, going from 100 million to 150 million registrations is a 50% advance. However, it will be just a 17% improvement as we go from 300 million to 350 million.

I have no doubt that Facebook is growing. Any of the nearly 350 million users on the site can see that firsthand. Old acquaintances keep popping up. The social-gaming element is so huge that Electronic Arts (NASDAQ:ERTS) agreed to pay as much as $400 million for Playfish this month. Playfish's titles are enjoyed by 60 million active gamers through Apple (NASDAQ:AAPL) iPhones and News Corp.'s (NYSE:NWS) MySpace social network, but its real buzz comes from Facebook hits Pet Society, Restaurant City, and Country Story.

Microsoft (NASDAQ:MSFT) may have been ridiculed for paying $240 million for a mere 1.6% stake in Facebook two years ago, but securing advertising rights on the globally relevant site has to have Microsoft laughing all the way to the bank.

Every passing day without Zuckerberg's "350 Million and On" blog entry is going to arm social-networking cynics with ammo, but bears shouldn't rush to a swift judgment here. If the users on the site are spending more time on Facebook than they used to, that would actually be even more important than just a nice, round milestone.

Hopefully Zuckerberg is cracking his knuckles for a new blog entry before Thanksgiving. A little color on member usage -- beyond the raw registered user mark -- would be sorely appreciated.