Aye, I know you can do it with a mass fabricator, but each diamond requires 9 UU-Matter, and even with several overclocked recyclers feeding into the mass-fab, it takes foreeeeeeeeeeeeever to be able to make anything decent out of it. It took me about 1 Minecraft day to get a piece of iridum ore (which requires 7 UU-Matter) for my quantum armor. In one Minecraft day, my current setup's given me 5 diamonds, and its not like coal and gravel are particularly difficult to find, let alone acquire, given that I've got a full compliment of red matter tools, not to mention 5 alchemy bags.
Hell, I've been spending a lot of my time crystal hunting, as I'm finally getting into Thaumcraft.