I actually just found out about this. I noticed degradation in my browsing experience over the past months but I have never really given it much thought until I noticed the new Bill Protect page (formerly "Anti Bill Shock Guarantee" page).
It says that once you have used up your GoSURF allocation and has reached the Bill Protect value of P1500, users will be throttled down to 128kbps (max).
I agree with you, ajacantre. Subscribers were not informed about this change.