I wote a bit about ODB++ back in October. Nothing has really changed much sice then. I'm just clarifying a few things.
First, I want to put more emphasis on the use of ODB++. In addition to being benificial to the manufatcuring process, it can make your job a little easier. If you send us ODB++, you do not need to send either the Centroid or Gerber files. The ODB++ replaces both.
Eagle CAD does not have an ODB++ export. However, the Eagle .brd file will work too. You can send us the .brd instead of the Centroid and Gerber files.
If you can't send either of those formats, we still need the Centroid and Gerbers (top copper, bottom copper, solderpaste stencil, silkscreen and solder mask layers).
I am not a number, I am a free man!