Have you got a source for this? If this is true, I'll be going to Three as well
http://community.giffgaff.com/t5/Contribute/Upcoming-goodybag-changes/td-p/14395647
3. To protect your data experience, even during the busiest hours of the day, we will add the following Traffic Flow measures to all of our unlimited data goodybags:
a) Where members are using more than their fair share of network resource during the busiest hours, a 300 kilobits per second (kbps) restriction will be introduced for the remainder of the peak period. This speed will ensure that members are able to use the internet but with less impact on other members.
b) A peer to peer speed restriction of 100 kbps during peak hours will also be introduced for these members.
Dunno where 3GB allowance came from though.