Well how hard is it to drive two bolts in orbit? Suni Williams and Aki Hoshide prove that it could be THAT hard. The spacewalk is the third longest ever (8 hours, 17 minutes), but the duo failed to install the new power box on the ISS (and had difficulty removing the old one). Only one other task was completed, which means another EVA is in order (particularly because the not installed MBSU means that the ISS is now down to single-fault tolerant for the power supply system).
NASASpaceflight.com: Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS
NASASpaceflight.com: Astronaut duo complete challenging first post-Shuttle US spacewalk on ISS