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bebologo1221.pngSocial network Bebo has just announced that its users have installed third-party applications 4,250,409 times since the site launched its developer platform last week.

This install number is significant, as it shows Bebo users want these applications nearly as much as Facebook users have. It also shows that applications developers on Facebook can expand beyond their Facebook audiences.

For sake of comparison, the most popular applications on Facebook grew to millions of users within a couple weeks of that sites platform launch on May 24. (See our earlier coverage of companies like iLike and RockYou.)

“Install” refers to each instance in which a user adds an application to their profile–such as adding a box to show their favorite music clips.

Measuring installs is a less stringent measure of popularity than Facebook’s current method, which calculates the percentage of people using an application on any given day (from the total number who’ve installed that application).

Bebo has developed its own developer platform to be Facebook’s, so many of Bebo’s 35 current application partners simply took their Facebook applications to Bebo. Unlike Facebook, Bebo has carefully restricted its platform to these partners and isn’t yet open to every interested developer. It will be after this initial phase, the company tells us.

The San Francisco company is also part of a rival developer platform effort called OpenSocial, which is led by Google. OpenSocial is still a work in progress, although it has some applications live on some social networks already, such as iLike on Hi5, as of yesterday.

The larger question, of course, is how much these applications are worth, even if they get big and span social networks.

That question is no doubt on Bebo’s mind. It has begun working with a bank, purportedly to help it raise more money–not to sell (our coverage).

Bebo applications range from simple boxes on a user profile that display music clips or a daily quote, to multiplayer games. One of the more interesting examples is Gaia OMG, an instant messaging application created by teen virtual world Gaia Online. You log into Gaia OMG within Bebo, using Gaia ID, then you can instant message with other Gaia and Bebo users and earn points for buying virtual goods in Gaia (a virtual hat for your Gaia avatar, for example).

Launch partners included NBC Universal, CBS, NBA, Yahoo!, The Gap, Flixster, Gaia Online, RockYou, Slide, BeFunky, iLike, WidgetBox, Wallop and more.