From top and bottom hits, we'd feel confident in the G-Form's ability to cushion a blow. The company has shown videos of its products protecting an iPad from a falling bowling ball, and while we didn't go that far in our testing, a test MacBook did survive a couple of desk-height falls.
Note, however, that these falls were into the flat face of the laptop/case combo. Less protection is offered if your laptop happens to land on the corner. Recently, one of our ZDNet colleagues had a G-Form iPad accidentally land squarely on a corner in an impromptu drop test, and the results were not pretty. The company says G-Form cases (at least the iPad versions) are being updated with a Poron XRD bumper insert under the zipper, but our laptop case didn't include that.
Still, some common sense is required to get the most out of any protective sleeve or case, and the Extreme Sleeve can certainly offer some peace of mind if you're worried about crushing or banging damage to your laptop. G-Form offers a limited lifetime warranty on the Extreme Sleeve, but note that this refers to the case itself, not to any electronics you pack inside of it. The company says, "Although we are confident that G-Form provides the best protection available, we can't guarantee your electronics from damage from any specific drop or impact in our Extreme Sleeve whether accidental or intentional."