Hello joomblaster, and welcome to the forums.
The discussion here may be a bit confusing. One member is saying that backlinks are updated every two weeks - but that's not the same as saying how often Penguin USES the refreshed backlink data. In fact, he didn't make it clear whether he is talking about the link: operator or the Webmaster Tools data.
Here's what we do know for sure: there has been only one Penguin data refresh, on May 26. And that was a full month after the first Penguin run on April 24. We keep track of Google's major Updates here: [webmasterworld.com...]
Adding even more complication to the picture, Penguin clearly runs on a lot more than just backlinks. The discussions are all over the forum and you can find them using our Site Search [webmasterworld.com]