For those who haven't seent it yet, Giffgaff have extended their free data by another 4 days.
Quote from
http://giffgaff.com/index/pricing:-
Free Mobile Internet:
You lucky giffgaff pioneers can even
enjoy free UK mobile Internet up to the 04 APR 2011. After that date, mobile Internet will be charged at 20p a day (if you use less than 1MB/day you'll pay less than 20p and if you go over 20MB you'll be charged extra at 20p/MB).
But all our goodybags that include unlimited Internet will continue including unlimited Internet after the 04 APR 2011.