IMO, Canon's lens/flash rebates no longer offer a meaningful incentive to purchase the products offered. I bought my 85mm f1.2L II a while back with a $130 rebate, which was a real rebate off the then-current street price. Today, even though the $150 rebate sounds appealing, in reality it's only a $50 rebate compared to last week's street price. Canon's 'minimum advertised price' policy has gutted the rebate programs.
Say I wanted the 70-300mm f/4-5.6L IS. A couple of days ago, everyone was selling it for $1519. Today, the price is $1599 and the $100 rebate only brings a net $20 savings. Heck, that's not even enough to cover a decent bottle of champagne to celebrate the purchase, so why bother?