Forget about seeing Facebook (NYSE: FB) become the next MySpace. Digg, once a popular news-sharing site, already has that dubious honor. New York's Betaworks has purchased the company for just $500,000, The Wall Street Journal reports.

Talk about a fall from grace. At one point, Digg was attracting 17 million monthly visitors and had Microsoft (Nasdaq: MSFT), Google (Nasdaq: GOOG), and Yahoo! battling over the rights to place contextual marketing on the site.

Venture capitalists also loved Digg. All told, the company raised $45 million in equity financing from the likes of Greylock Partners, LinkedIn co-founder Reid Hoffman, and Netscape co-founder Marc Andreessen, the Journal reports. Betaworks won't be giving any of them much of a return.

MySpace offers a similarly sad tale. After several years of leading the way on social media, the network, which gained popularity as a place for musicians to market their work, last June sold for $35 million to a group that included performer Justin Timberlake.

But don't weep for either Digg or MySpace. Founders of both companies have done well enough. News Corp. (Nasdaq: NWS) initially paid more than $500 million to acquire MySpace in 2005, while Digg founder Kevin Rose has made successful bets on a number of start-ups you know, including Foursquare, Twitter, and Zynga. He's also working at Google in an as-yet undisclosed capacity.

Nevertheless, the point remains. Investing in innovators such as Digg and MySpace is dangerous, because what looks like a sure thing -- (cough) Research In Motion (cough) -- could be irrelevant within a few years.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team and the Motley Fool Supernova Odyssey I mission. He owned shares of Google at the time of publication. Check out Tim's Web home, portfolio holdings, and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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