Stop me if you've heard this one before: Facebook's (NASDAQ:FB) IPO didn't go so hot. OK, that might not be news to you, but the social networker also saw another relatively dull debut today (albeit a less significant one than being the largest IPO of all time).

A week ago, Nasdaq OMX Group (NASDAQ:NDAQ) said it would be adding Facebook to its widely followed Nasdaq-100 index, which tracks the 100 largest non-financial stocks on the exchange. That's generally seen as having the potential to provide some support for stocks, since mutual funds and ETFs that track the index are then required to add the company to their portfolios. In contrast, Facebook shares actually fell by 2.7% the day after the announcement, and are down over 1% today, which is the first day it has traded within the index.

One of the largest ETFs that tracks the Nasdaq-100 is PowerSharesQQQ (NASDAQ:QQQ), which has about $30.8 billion in assets under management. Facebook is now the 10th largest tech stock within QQQ, at 1% of assets, while Apple (NASDAQ:AAPL) dominates the portfolio at 16.7% of assets. Microsoft (NASDAQ:MSFT) trails at a distant second, accounting for 7.5% of assets. After Microsoft comes Google (NASDAQ:GOOGL) at 6% of assets.

That has some diversification implications for tech investors that may own QQQ as well as any of the aforementioned tech giants, because they may be more overweight in those stocks than they realize since those three companies combined are over 30% of the fund's holdings.

Infosys decided to switch exchanges, making some room for Facebook's inclusion in the Nasdaq-100. Facebook will carry more weight than Infosys did, since the index is market-cap weighted and Facebook's valuation is over twice as large.

That difference is unlikely to affect the weighting of other components, though, since the Nasdaq-100's combined market cap is nearly $3 trillion.

The news doesn't affect Facebook's long-term fundamentals, but being included in such a widely followed index does come with a certain amount of prestige. Nasdaq certainly benefits from that ubiquity in the form of licensing fees it collects.

Facebook has rallied an incredible 57% from its lows as its prospects at new revenue streams continue improving. Those new potential businesses are what count for investors, and hopefully the company will even get back to its IPO price in the foreseeable future.

Fool contributor Evan Niu, CFA, owns shares of PowerShares QQQ Trust, Series 1 (ETF) and Apple. The Motley Fool owns shares of Apple, Facebook, Google, and Microsoft and has the following options: long JAN 2014 $20.00 calls on Facebook. Motley Fool newsletter services recommend Apple, Facebook, Google, and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.