????以Facebook為例，它目前的股價是過去12個月營收的231倍，是2013年預計營收的71倍。標普（The S&P 500's）的平均市盈率是19。而Facebook令人暈眩的股價存在的基礎是它未來數的年營收能夠繼續快速增長這個樂觀的預期。不過迄今為止，事實證明這家公司的營收并不容易準確估測。而根據歷史經驗已經證明，將股價寄托于未來數年的利潤這種做法充滿了風險。

????但是，從網絡股的股價看，網絡股的投資者中采用這種計算方式的卻大有人在。有些公司的市盈率甚至達到了三位數。比如LinkedIn的累計市盈率就高達926，2013年的預估市盈率也高達159。網飛公司（Netflix）2013年的預估市盈率更高：218。而像Zillow和Yelp的市值就更難評估了，因為它們預計今年也難見到盈利，但它們的股價卻像是它們的利潤馬上就要飛速增長似的。

????網絡股的這種集體大漲源于對一個特定產業的押注，即移動設備將成為廣告服務的主要領地。現在很多人手里都會拿著個手機，每天總要看上十多次，導致大家紛紛想在移動廣告服務領域搶一杯羹。同時，由于用戶日常活動的相關數據被細致追蹤，也使這些廣告的傳播目標更加精準了。

????但是很多事情可能會過猶不及。對狂轟濫炸的廣告感到厭倦可能會讓用戶遠離那些靠拼命彈出廣告來掙錢的應用和服務。而公眾為保護隱私而反對廣告泛濫，或是政府出臺限制企業跟蹤個人信息的法規都會影響到廣告鎖定用戶的精準程度。廣告市場可能會比很多人所預計的更快走向飽和。一句話，目前股價上漲的基礎是是一個盡管前景看好、但尚未經過驗證的商業模式。

????如果說這種說法聽起來像是互聯網泡沫2.0版，那也未必。泡沫往往是大規模發生的，即整個市場都被非理性的狂熱心態席卷后才會出現。我們現在所看到的是，在一個相對較小的特定市場中，有人摒棄了理性的基本面分析，轉而依靠非理性的空頭支票來炒作股價。但這種做法并不意味著它是理智的投資行為，也不能說目前的這種非理性不會在某個時候變成狂熱。

????可能掀起一場狂熱的一大因素是個人投資者是否會受到Facebook及其同類公司飛漲的股價誘惑而紛紛入市。過去15年里，這些投資者兩度飽受重創，一次是互聯網泡沫的幻滅，第二次是規模更大的房地產泡沫破滅。畢竟，現在這些公司也是很多人熟悉、而且天天使用的品牌，而小投資者往往更傾向于投資自己熟悉的品牌。

????這種投資方式本身不算下策。但更困難、同時也許是也更重要的一點是，搞清楚什么時候一只股票的價位太高，已經不再適合買入。就算網絡股目前還沒有到達高點，我們離那一天也已經不遠了。（財富中文網）

????譯者：清遠???

????Consider Facebook. The stock is currently trading at 231 times its earnings over the past 12 months and 71 times its estimated earnings for 2013. The S&P 500's (SPX) average P/E ratio is 19. Facebook's heady price is based on optimism that its earnings will grow quickly in coming years. But the company's earnings have proven hard to predict so far. And historically, the practice of basing a stock's value on profits that will come several years down the road has proven risky at best.

????Yet that very attitude seems to have grown commonplace among investors in web stocks, as their valuations show. Some are at triple-digit valuations. LinkedIn has a trailing P/E of 926 and an estimated 2013 P/E of 159. Netflix's estimated 2013 P/E is even higher: 218. Others like Zillow and Yelp are harder to value, since they aren't expected to post a profit this year and yet are priced as if they will soon see profits grow quickly.

????The web rally is a sector-wide bet that mobile devices will become a prime venue for serving ads. Many people have a mobile phone constantly at hand and gaze into them dozens of times a day, making the serving of on-the-go ads a snap and also improving the targeting of those ads as user data on their daily activities is tracked in detail.

????But a lot of things could go wrong. Ad fatigue may steer users away from apps and services that advertise aggressively to keep their profits growing. A privacy backlash or regulation limiting companies' ability to track personal data could limit how effective targeted ads become. The ad market could become saturated faster than many are anticipating. In short, stock prices are rising on an unproven, if promising, business model.

????If this sounds like Internet Bubble 2.0, it's not. Bubbles happen on broad scales, where an irrational and momentum-minded mindset takes over an entire market. What we're seeing is a departure from sane fundamental analysis in favor of irrational hope among a relatively small segment of the market. But that doesn't mean it's sensible investing, or that the irrationality won't grow in time into a mania.

????One thing that could help spur a mania is if individual investors -- burned twice in the past 15 years by the dot-com bubble and the fallout of the even bigger housing bubble -- are seduced by soaring prices of Facebook and its peers. After all, these are also brands that many people are familiar with and use everyday. And small investors are comfortable investing in what they know.

????Which in itself isn't a bad approach to investing. What is harder -- but perhaps more important -- to know is when a stock is too expensive to bother buying. We may be reaching that point soon with web stocks, if we're not there already.