rockyoulogo.pngRockYou, the company behind popular Facebook applications and Myspace Flash widgets, may soon pass its arch-rival Slide to be the largest widget-maker in the world.

Some have accurately called such Facebook applications “mostly silly, useless and time-wasting” — yet this virtual real estate may be worth a lot one day. RockYou claims it is quickly growing revenue through running advertising across applications.

The San Mateo company’s “SuperWall” Facebook application has just passed Slide‘s “FunWall” application in number of daily active Facebook users — 3,186,833 versus 2,951,078. Like Facebook’s own Wall feature but with a few bells and whistles, these applications allow users to comment, post videos and share other information on each others Facebook profiles.

Slide and Rockyou began as Flash widgets that let users create and share online photo albums on their Myspace pages. The companies then expanded to other social networks, like Hi5 and Bebo.

Both companies took early advantage of Facebook’s developer platform, launched in March, to build simple, game-like applications. These companies grew quickly through a number of tricks, such as advertising new, less popular applications within larger, existing applications to grow their overall traffic.

External measures of these companies are hard to come by. Comscore, a leading web traffic measurement company, released a widget measurement service in June that showed Slide had more than 117 million people viewing its widgets in April. Then, Rockyou had 82 million. That number has risen to 104 million as of last month, the company tells us.

If you trust Alexa, another web traffic measurement service that many have found to be wildly inaccurate, RockYou’s home site is now reaching 0.49 percent of internet users — an 112 percent increase over the last three months — a reach that’s slightly larger than Slide’s.

Compete, another web measurement, shows a less fantastic — but still positive — view of RockYou’s growth: