On the Zend Developer Zone Ralph Schindler has announced this month's bug hunt days for the Zend Framework:

For those who haven't put the reoccurring event in their calendar, this announcement is for you: Zend Framework Monthly Bug-hunt is here again! This Thursday, Friday and Saturday of March (the 24th, 25th and 26th 2011), we'll be hosting our monthly bug hunt. For those of you unfamiliar with the event, each month, we organize the community to help reduce the number of open issues reported against the framework.

He mentions the winners of last month's event - Benoit Durand and Ramon Henrique Ornelas - and a link to their guide on how you can get started and get involved with this month's event (starting with getting a CLA on file).