LinkedIn’s IPO debuted on the New York Stock Exchange under the symbol “LNKD.” Priced at $45 a share, the whole company is valued at close to $4.3 billion.

This would make it the largest tech IPO since Google in 2004. It’ll also be valued at an incredible 260 times its 2010 earnings. Meanwhile, Facebook is valued around $50 billion, at a P/E ratio of 80 (according to the 2010 profit reported here), on the secondary market.

The incredible valuations and hype around these two internet tech companies begs the following question: are we in another tech bubble?

In short, the answer is no – at least not yet and not in the United States.

The two US companies in question, Facebook and LinkedIn, are the real deal. They are profitable and dominate their respective spaces. Facebook is already the second most popular website in the US and LinkedIn is the 26th most popular.

Moreover, they’re leaders in the world of Web 2.0, which many experts believe is the platform of the future.

Their valuation may seem steep, especially for LinkedIn. However, it’s just a case of investors chasing hot companies rather than an entire sector. It’ll only become a bubble when, for example, investors begin to buy any company, even a low quality one, that is remotely related to social media.

Public participation is also limited compared to the late 1990s – the frenzy is more confined to the institutional side. The damage, if there is any, will therefore also be limited.