I agree there's another bubble inflating with social networking - but I think some lessons recently learned during the first internet boom and bust are making this one a little harder to pop.
There are some very good / valid / practical / monitizable (is that a word?) aspects to social networking - but many people and companies are blindly jumping into it without seeing it for what it is....a way to accelerate reach and reduce the time and "distance" between people.
Companies that look to social networking as a magic bullet for sales and marketing are missing the point. There are little or no barriers to doing it. If everyone is doing it / can do it, then there is little advantage. ...it becomes the norm, the baseline, not a boost above the crowd.
There is no substitute for having a polished product or service. Using social networking to engage customers, then refine the product or service, is a no-brainer. Many people and companies clamoring to go "social" are doing it for the sake of doing it.
...the first internet boom similarly had everyone and their cat thinking that a website was the magic key to riches. ....then they figured out that a website isn't a whole lot different than a listing in the yellow pages....but -woooo! GLOBAL! (yipeee!)
Kids, the "Yellow Pages" are an antiquated version of a website, but printed on paper, with an alphabetical and topical list of businesses. Similarly, the "White Pages" are the analog of social networking.
...at some point, the social networking sites will run out of excitement / frenzy money. Social Networking fatigue and malaise will set in, people (people that pay bills for massive server arrays, bandwidth, data centers, utility bills, etc.) will ask if they can afford to keep doing it without charging people something.
...and then, pop!