As is the case in many large SUVs, despite having room for seven people in its three rows, the GL leaves little room for luggage when all its seats are in use; there's just 14.3 cubic feet behind the third row. There's some space underneath the cargo floor, but it's only suitable for smaller things, like jumper cables.
Full-Size Luxury SUV Cargo Room Compared (cu. ft.)
Behind 3rd Row Behind 2nd Row Behind 1st Row
2011 Cadillac Escalade 16.9 60.3 108.9
2011 Infiniti QX56 16.6 49.6 95.1
2011 Lexus LX 570 15.5 41 83.1
2011 Mercedes-Benz GL-Class 14.3 43.8 83.3
Manufacturer data

The GL has a standard power-operated third row, which is a great feature because it transforms what could be a cumbersome process of folding and opening the third row into a simple operation. It even works when the second row is reclined.