LinkedIn, a business network that's hugely popular among Silicon Valley's top private equity investors, yesterday opened its service to third-party software developers, in what looks like an attempt to be more like Twitter.

That's understandable. Twitter recently took in $100 million in fresh capital from venture investors, who valued the business at a cool $1 billion.

A warming IPO market could multiply that price tag, and boost interest in LinkedIn in the process. For example, Mead Johnson Nutrition (NYSE:MJN) is up more than 80% since its offering in February. (NASDAQ:CYOU) is up almost 70%. And while Open Table (NASDAQ:OPEN) hasn't done much since coming to market in May, early interest from private bidders boosted its debut from $12 to $20 a share.

Of course, there's more than valuation envy behind LinkedIn's decision to court developers. After all, its network was valued at $1 billion last summer. More likely, this move recognizes what those of us following social media have long known -- that applications create value as much as users do.

Gimme me an A! Gimme a P! Gimme an I!
Again, look at Twitter. Power users of the microblogging service often use multiple applications to sign into the service. TweetDeck and Seesmic Desktop are two of the most common, but there are also specialized services such as StockTwits.

Twitter's open programming interface -- or API -- allows these services to exist. That could open the way for the microblogger to rake in revenue via contextual ads, threatening Google (NASDAQ:GOOG), Microsoft (NASDAQ:MSFT), and Yahoo! (NASDAQ:YHOO), among others.

LinkedIn now has an API of its own, giving developers the tools to write social business software for one of the Web's largest and most active business networks. What investor wouldn't want a piece of that?

But that's just my take. Would you invest in LinkedIn if given the chance? Make yourself heard using the comments box below.

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Fool contributor Tim Beyers owned shares of Google at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. The Fool's disclosure policy prefers eggnog, actually.