There is nothing complicated about a shock absorber. It is a mature technology. I can understand a single shock failing due to a manufacturing defect, but for two to fail, on the same vehicle, within 30 miles of installation, is an extremely unlikely event.
My guess would be either the installation was done improperly or the mounting points are not to spec. Was your MO ever involved in a rear-end accident?
2005 SL AWD, Platinum
-OEM HID conversion & HID fogs
-OEM iPod interface
-Upgraded (non-Bose) speakers - Pioneer TS-A1702C & TS-G1643R
-Muth signal mirrors
-Valley Industries hitch and wiring harness
-Aluminum fuel tank shields