OpenTable’s 2009 IPO marked the return of the Internet IPO in the wake of the recession. During the two quarters before OpenTable went public, no venture-backed startups staged an IPO. OpenTable showed that not only were the markets safe for a growing, profitable Internet company, but its surging stock price since then helped warm the waters for others like LinkedIn and Zillow to jump in.

OpenTable was a gift-wrapped IPO, just what the market needed to seduce institutional investors into the notion that web2.0 isn’t just a buzzword-turned-market-mania that given would time burn itself out. Last month, the stock traded as high as $118.66 a share, nearly six times its $20 offering price.

But in the last month, the sentiment has changed around OpenTable. And that shift may reflect a growing sense of unease in the inflated valuations of web companies like Facebook as they head for the public markets. OpenTable’s stock has lost more than a fifth of its peak value, and short interest on the stock is rising, suggesting bearish investors are betting on further declines to come.

On the one hand, the decline isn’t surprising. OpenTable’s stock was trading at 101 times its estimated 2011 earnings a month ago. And the correction brought the stock back down to levels it first reached in early February — that is, to returns still enviable for a two-year period. On the other hand, the stock is still trading at 82 times its 2011 earnings. Google (GOOG), by contrast, is trading at 16 times earnings.

And short interest, shares held by short sellers in expectation of a decline, rose to 5.7 million shares at the end of April from 4 million shares two months earlier. That’s equal to 27% of OpenTable’s stock float, which means that more than 1 in 4 OpenTable shares available for trading is held by someone expecting the stock to decline.

OpenTable has faced a high short interest before, but the enthusiasm of its bullish investors always prevailed. That changed earlier this month, when OpenTable announced its quarterly earnings as well as the news that its CEO Jeff Jordan would step down.

Jordan, an eBay (EBAY) veteran before joining OpenTable, will become its executive chairman, handing the reins to Matthew Roberts, its CFO since 2005. The news came in the midst of what on the surface seemed a strong financial quarter, with OpenTable’s revenue rising 60% and the 28-cents-a-share earnings coming in five cents stronger than estimates.

As good as Jordan’s name is in Silicon Valley, news of the change in CEOs shouldn’t have caused the stock to plunge. The financial report also showed its net profit margin at 12% in the first quarter, flat with the year-ago figure but down from 16% in the previous quarter. Some analysts thought the 19% operating margins was lower than they expected.

Profit growth had powered OpenTable’s stock rally. The company’s business plan wasn’t radically innovative. Rather, its success showed that there are corners of the business world — like independent restaurants — that haven’t yet been adequately been brought online. And that companies that mine these untapped areas of e-commerce can, as they scale up, grow revenue faster than operating costs.But OpenTable’s profits are remaining flat at best. Seeing a valued CEO depart at the moment when investors are hoping to see margins grow took some wind out of OpenTable’s power rally. Once that happened, the bearish short sellers stepped in, and the bulls couldn’t overpower them this time.

All OpenTable needs is an exceptionally strong quarter to reverse the stock decline. But the correction is a reminder that OpenTable, no matter how well it’s managed, can’t justify a triple-digit P/E ratio. If bears and short sellers win out, the company may go from a well run business that is overvalued to a company that is seeing its stock plummeting even though it’s doing everything right.

And that in turn could dampen the market’s enthusiasm for the other highly-valued web stocks that want a piece of the hot IPO market.