Last May, YouTube invited a select group of users to begin sharing in revenue from ads that run along with their content. Now, the user-gen site is opening up its “partner program,” giving all users in the U.S. and Canada the chance to compete for tapping the revenue from its overlay system. YouTube will judge its next round of partners according to the amount of pageviews and subscribers they attract. So far, 100 users have been added to the program, up from about 40, though YouTube doesn’t say how many participants are currently involved. Over the next few months, YouTube plans to make partner membership available internationally.

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YouTube has been vague about how much revenue they’ve shared with its users. A representative for the Google-owned site told me that YouTube “shares the majority of the revenue with our partners.” The user-gen site also says that “millions of video views” are making money every week for their posters and those who regularly produce videos with over one million views are earning several thousand dollars per month. But an immediate windfall in ad revenue from user-generated content is probably an afterthought at the moment, as YouTube ultimately hopes that by encouraging users to consider ad revenue, they will create a more comfortable environment for advertisers on the site in general.

So far, the biggest channels, which are ranked weekly here, are dominated by likes of gossip blogger PerezHilton, the NBA, CBS, Universal Music Group and National Geographic. More details on YouTube’s blog and in its release.