I wrote about Facebook's IPO back in May pointing out how unbelievable it was to me that a company that started back in 2003 and really doesn't make anything of substance or have a very compelling revenue model could go public at a $100 billion dollar valuation. I ended the post by saying, "the world has changed".

Well, maybe not. A lot has changed for Facebook since then (see stock price chart above).

Their market cap is now below $40 billion and the consensus seems to be that their stock price is going to continue to fall. That said, their shares are still trading at around 32 times earnings -- so there's still a decent amount of hype around this IPO.

One of the primary reasons for all of the hype is that Facebook is so widely known and widely used. They have hundreds of millions of users; many of them use the product several times a day, every day. And the vast majority of these users know absolutely nothing about investing. But because they use the product and know the product, they were compelled to buy some shares. As a result, the company was hugely overvalued following its IPO.

Contrast this with Globus Medical, a medical device company that went public on Friday with virtually no hype. It’s unlikely we’ll see this stock nosedive like Facebook. They have a fraction of the customers that Facebook has – they make medical devices used in spinal surgery – so there are far fewer people interested in owning a piece of the company. There’s far less hype.

There have been literally thousands of consumer web services started and funded over the last couple of years. Many of these companies have millions of users and no revenue or compelling revenue model. As a result, I’d expect to see more and more companies go public in the near future with inflated valuations that are propped up by their user base.

The Facebook IPO underscores a good lesson for amateur investors: just because you use a product every day doesn’t mean it should be a part of your portfolio.