Through 2005 the GEC and EGC have always been separate requirements.This has always been interpreted to represent two separate conductors. These conductors can share the same raceway as long as the raceway is bonded according to 250.
In the 2008 however, article 690.47 a single conductor may used for both purposes.
(excerpt from John Wiles' Checklist URL below)
9. GROUNDING
• Only one bonding conductor (grounded conductor to ground) for dc circuits and one
bonding conductor for ac circuits (neutral to ground) for system grounding? [250] Note:
The dc bonds may be located inside inverters or in ground-fault protection devices.
• AC and dc grounding electrode conductors connected properly? They may be
connected to the same grounding electrode system (ground rod). Separate electrodes,
if used, must be bonded together. [690.41,47] The 2008 NEC in 690.47 allows a
combined dc grounding electrode conductor and an ac equipment-grounding
electrode, but the conditions and requirements are numerous. {690.47}
• Equipment grounding conductors properly sized (even on ungrounded, low-voltage
systems)? [690.43]
• Disconnects and overcurrent in both of the ungrounded conductors in each circuit on
12-volt, ungrounded systems? [240.20(A)], [690.41]
• Bonding fittings used with metal conduits when dc system voltage is more than 250V
dc? [250.97]
(From John Wiles at NMSU PV checklist
http://www.nmsu.edu/~tdi/pdf-resources/INSPECTOR_CHECKLIST_6-23-06.pdf