Topic: Defining the success of a beta test program

I've found literature on this surprising elusive on-line thus far, so I'd like to ask the question of any interested parties here.

How would you define the success of a beta test program?

Getting into specifics if I have for a given program that's run for a given time, some data like so:

Number of beta testers who have installed activated the product

Number who have responded to a feedback survey form

Number of bugs they have submitted

Number of staff you have dedicated to finding, inviting and supporting beta testers in the field.

I have thus far only one reference, being Joel on SoOftware who'd suggest that 1 in 5 of the pople who have the produce will actually feedback and submt any bugs. I'm wondering if there is any more industry data on beta test programs and how to gauge if yours is being exceedingly successful, unsuccessful or on par.