In what there calling "The Facebook Effect," metrics firm Quantcast says widgets developed on the Facebook platform are driving substantial traffic spikes for the websites they’re connected to.

The company’s not speaking for all websites that have developed applications for Facebook, just for a few already somewhat well-known clients. But not one of the ones measured saw a traffic increase of less than 98 percent.

Popular "personal media network" Slide.com tripled its traffic, growing from 312,000 unique US visitors to 1.1 million since distributing apps on Facebook, an increase of 265 percent. Globally, daily unique visitors jumped from 753,000 to 2.3 million, an increase of 207 percent.

"Just six weeks into Facebook’s open platform initiative, we are seeing striking results," said Konrad Feldman, co-founder and CEO, Quantcast Corporation.

"The Facebook platform is driving substantial incremental traffic to application publishers’ Web sites, as consumers find new routes to exploring their wares."

Self-esteem regulation site HotOrNot.com doubled its daily unique visitors, increasing in the US from 182,000 to 350,000 (up 98%), and increasing from 289,000 globally to 722,000 (152%).

"Like many publishers, we have had a great response from the Facebook community," said James Hong, co-founder, HOTorNOT. "We are thrilled that in addition to distributing our application, Facebook’s open platform is helping us introduce our Web site to the next generation of Internet users."

RockYou, a distributer of "self-expression" widgets, spiked 228 percent in the US, and 339 percent globally, increasing, in total, from 286,000 visitors to 1.3 million.

"Facebook has been an instrumental platform to leverage our applications (widgets) and viral growth expertise," said Jia Shen, CTO and co-founder, RockYou. "We’ve been able to successfully create the deep social experiences we are committed to. Already, 30% of user profiles on Facebook showcase a RockYou application.