For all the excitement about Facebook’s explosive growth, it somehow feels like a huge fad that could disappear or, at least, dissipate, if something cooler comes rumbling over the horizon. When parents and businesses start embracing Facebook, it’s probably the time for the new “bar” down the street to suddenly get “hot”.

Based on posts by Brad Feld and Fred Wilson, here’s my list of why Facebook could go from fast-growing to so yesterday sooner than we think:

1. The evolution of its business model: What many people like about Facebook is it has a clean, easy-to-access look and feel. You log in, you quickly see what’s been happening in your world, you do your thing. What happens when Facebook starts to introduce more advertising into the mix so it can start taking advantage of its billions of pageviews? Suddenly, the lean look disappears as the business model starts to move onto the scene.

2. In-box Contamination: Facebook works right now because you decide how big or small you want your community to be. As much as Facebook is hot, it’s still manageable in terms of deciding who you want to invite/accept as a friend. But what happens – as Fred Wilson points out – when you’re swamped with Facebook invites? Suddenly, Facebook runs into the same annoying problem as Plaxo and LinkedIn as your in-box gets invitation contamination.

3. Application noise. For all the excitement about Facebook opening its API to the world, it’s also more noise for users. I can’t tell you how many multiple invitations I’ve got for Flixster, for example. It’s already getting annoying. This is an issue Fred Wilson focused on.

4. The IPO: There’s plenty of speculation Facebook could go public later year – a move that would allow Facebook founder Mark Zuckerberg to pull some money out of the company without giving up control. Once Facebook becomes a business that needs to meet the lofty expectations of Wall St., it’s about the same time that the fun and all-for-one, one-for-all mentality starts to disappear.

5. Facebook Fatigue: Right now, Facebook is fun, it’s new, it’s a novelty but how useful is it really? How long before the millions of people who have piled into Facebook stop checking their profiles every day or, for that matter, every week.

Don’t get me wrong; I think Facebook is a fascinating social phenomena as well as an amazing social networking tool. Maybe I’m being too pragmatic or a non-believer but every party reaches a zenith before leveling out so I’m curious about when that time comes for Facebook.

Note: For an interesting take on Facebook’s future, check out Richard Stelmach’s post on what Facebook could look like in 40 years.

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