Apple (AAPL) is a monolith in the equities market and the stock has played a major role in bolstering technology indices and exchange-traded funds. Consequently, ETF investors who want to take on a broad exposure to the technology sector may want to consider the stock's impact, lest you find yourself over-exposed to a single stock.

Apple is a phenomenal growth story, surging 50% year-to-date, and is now the largest company with a market capitalization closing in on $600 billion. Due to its large size, the single component has accounted for a significant portion of most broad market indices, previously making up over 20% of some indices. However, due to special rebalancing, AAPL shares have been reduced, but they still remain among the top holdings in Nasadq indices. For instance, the Nasdaq Composite Index has a 9.3% weighting in AAPL, the largest component stock. As a result, the Nasdaq Composite has increased 17% year-to-date and the Nasdaq-100 has tacked on 19% year-to-date, compared to the 11% rise in the S&P 500 and the 8% gain in the Dow.

The robust performance in tech-related indices is also reflected in technology ETFs. For example, the SPDR Technology Select Sector Fund ETF (XLK), which has a 19.1% weighting in AAPL, is up 18.4%, Vanguard Information Technology ETF (VGT), which has about a 10% weighting in AAPL, gained 19.3% year-to-date and iShares Dow Jones U.S. Technology Index Fund ETF (IYW), which has a 22.1% weighting in AAPL, is up 19.8% year-to-date. Furthermore, the PowerShares QQQ Trust (QQQ) - a fund that follows the Nasadaq-100 Index - also allocates an 18.7% weighting in AAPL and has seen its prices rise 19.9% year-to-date.

With most tech sector market-cap weighted ETFs holding around 20% of their overall portfolio in AAPL stocks, potential investors should consider the diversification ramifications, specifically the overconcentration of one security in one's overall financial portfolio. This is particularly noteworthy as many analysts, investors and observers are pointing to Apple as the major benefactor of the impressive performance in broad indices - a previous Barclays report even highlights the fact that if AAPL were completely removed from the S&P 500, the estimated overall earnings growth would be closer to zero instead of 1.4% year-over-year for the first quarter. Bloomberg also notes that Apple's 653% vault in share prices since March 2009 accounts for 8% of the 103% climb in the S&P's performance.

Still, Apple has proven that it is generating the necessary revenue to justify its presence. The company is selling more iPads and iPhones and its products have only touched the surface of the vast Asian markets.

Nevertheless, even with the profits AAPL shares have provided, ETF investors should be aware of how much their overall portfolios are exposed to that single holding, especially if investors are supplementing their ETF investments with additional stock picks. The big concern here is that someday Apple may lose its leadership role and prove to be a burden on the overall markets -- then the heavy emphasis in AAPL shares will become more of a liability rather than a boon.

A large weighting in a specific stock is neither good nor bad, but investors should still be mindful of the consequences. On the other hand, investors seeking a more diversified ETF portfolio, without the heavy weighting in Apple, may consider equal-weight ETFs like the First Trust Nasdaq 100 Equal Weighted Index Fund (QQEW), First Trust Nasdaq 100 Technology Sector (QTEC) and the recently launched Direxion Nasdaq-100 Equal Weighted Index Shares (QQQE). These ETFs will provide investors with a flatter overview of the benchmarks, equally distributing the weighting among component stocks. It should be noted that while the market-cap methodology favors the giants and potentially the overvalued, over the long-term, the equal-weight methodology has historically outperformed since it provides a greater emphasis in small- and mid-cap stocks that have a higher potential for growth, compared to their larger, more established counterparts.