I actually PREFER refurbished iPhones. When a bootrom exploit for the iPhone 4S is released, I am going to buy a refurbished iPhone 4S.
Why do I prefer refurbished iDevices.
Simple./ refurbished iPhones had a previous owner. There is a chance that the previous owner jailbroke there device and saved SHSH blobs. With a brand new iPhone there is now way you can use the SHSH blobs of your old device, but buying a refurbished one means that the device may have SHSH from use of the previous owner. As it turns out, when an iPhone is rebuilt, any SHSH blobs saved for that device will remain to always work for that device.
And yes, all replacement iDevices are refurbished unless you received too many defected devices, in which case you can request to receive a brand new model.