I read somewhere that traditional hard drives do not fully saturate the capacity of USB 3.0. The poster's point was that, if a spinning drive could not saturate 3.0, then it will not saturate Thunderbolt, or even utilize it near its potential. Is this correct? Here's why I ask. I am looking for a portable external for my rMBP. I was going to get a Seagate GoFlex 1.5TB with the Thunderbolt adapter to utilize the speed and available ports. However, if the notion above is true then the adapter is useless where speed is concerned. It simply utilizes a thunderbolt port instead of a USB. Can one successfully utilize thunderbolt speeds with a spinning drive? I thought it could, so I guess I'm looking for confirmation contrary to the first paragraph. If so, what are other solutions to a bus powered 1TB-1.5TB drive with thunderbolt? Seagate adapter....Buffalo Mini Station...anything else? EDIT: ADDED: If USB 3.0, and subsequently TB, cannot saturate a spinning drive, then I'll be in the market for a USB 3.0 drive.