I set up a large quarry in the nether at like y100ish, power it with an energy tesseract and feed the results in to an enderchest, i have a sorting system at home to empty the enderchest recycle the netherack and i get a rather large amount of ore (especially at the 4:1 nether ratio) plus my normal world doesn't have a bunch of holes all over the place you can also gather obsidan from the lava if you make a water block from uu-matter first. :)