While it is possible to continue on any existing save you currently have, its recommended to start with a fresh world in 0.7. Drastic changes have been made to the early game and world gen.
Power is primarily RF based now, especially in the early game. A machine called a CEF is used to transform RF into EU to power Gregtech machines. The quests will guide you through this.
Combined with the lossless cables, this should make Gregtech power management much less painful.
Energetic Alloy and Vibrant Alloy moved to later in progression.
Endergy Alloys added into progression. Better EnderIO Energy Conduits are now each built from the lower tiered Conduits.
Reworked a large number of the quests in the first two tabs to accommodate these changes.
Zinc (and therefore Sphalerite) have been added to the Overworld's ore gen. Tetrahedrite has been made to spawn deeper to increase its frequency.
Restored all of the XU2 generators to be craftable, as well as the Enchanter.
Dark Steel Ingots can be alloyed using Void Crystals as well as Obsidian now.