Though we have no confirmations that the price drops are permenant, we can probably assume them to last a long time if not forever. Canon has cut prices from $1000 on the higher-end lenses to $50 on the more affordable glass across their product line. In all, there are 26 lenses discounted as of today.
This is a complete list of the new prices, including how much they have been discounted:
Tilt Shift Lenses