In a world of fat numbers, Facebook's announcing that it has 500 million active users as of yesterday is impressive.

As the undisputed champ of social networking, Facebook has managed to sidestep the traps that befell Friendster (too soon) and News Corp.'s (NYSE: NWS) MySpace (too gaudy). Just a few weeks ago, AOL (NYSE: AOL) had to write off its $850 million purchase of Bebo as it asked a hedge fund to bury the body in exchange for what is essentially cab fare home.

Facebook appears to be on top of the world, but this also makes it an easy target. As the tag line for this fall's unauthorized -- and unflattering -- biopic The Social Network goes, "You don't get to 500 million friends without making a few enemies."

It's not just the movie. Headlines have been quick to pick up on the man alleging that he is entitled to 84% of Facebook and an American Customer Satisfaction Index survey of consumers that gave the sticky site an abysmal rating.

It isn't going to get any easier for Facebook, especially as it is dogged by privacy concerns and general disdain for top-of-the-heap websites.

This brings me to two simple words of advice for Facebook: Go public!

Once the ownership case is cleared, there is no reason for Facebook to hold off its publicly traded debut, which would let the public buy shares of the company. Resentment is only going to grow. The company's torrid growth is also starting to slow.

Really.

Let's go over Facebook's 100-million-member milestones, leading up to yesterday's juggernaut.

Date

Users

8/26/08

100 million

4/8/09

200 million

9/15/09

300 million

2/4/10

400 million

7/21/10

500 million

Source: blog.facebook.com.

It took slightly longer for Facebook to go from 400 million to 500 million than it did to reach the 300 million and 400 million marks. Registrations continue to head in the right direction, but growth has begun to decelerate.

This isn't problematic, necessarily. Active users are likely to be spending more time on the site than before, because they probably know more people on the site. A larger audience also attracts hungrier advertisers, something that has to be worrying Google (Nasdaq: GOOG), Yahoo! (Nasdaq: YHOO), and Microsoft (Nasdaq: MSFT), especially as search queries can now simply be voiced on the site for personal guidance and direction.

An IPO now makes sense. Not because I fear Facebook has jumped the shark, but because it would be disastrous if Facebook waits until it truly has peaked to go public. User growth will likely continue to decelerate. The critics will only get louder. The possibility that someone -- anyone -- will build out a Facebook killer, will never go away.

Kudos on the 500 million, Facebook. The next number that you should be thinking of is your publicly traded market valuation.

Should Facebook go public? Share your thoughts in the comments box below.