Over the last giffgaff payback period I actually earned an amazing £122! That was in only 6 months from December 2013 to May 2014. I have been earning a consistent £20 per month from just using the forum and I have had a few people sign up from my giffgaff referral links. You can potentially earn up to £30 in a month from using the forum, I think to get that extra £10 you have to post in the help section so this month that is what I am doing. I'll update if I do manage to earn the full £30.
I am still only buying the £10 goodybag every month so giffgaff are practically paying me to use their network!
Here is my referral link if anyone wants to join me and the rest of the giffgaff community on this awesome network!