I'm resurrecting this thread because I am now having the same issue with my 2011 iMac with a Samsung Bluray writer. I have a 7 port USB router, but the drive will not work with it. It reads slowly and then locks up programs such as dvdfab. I don't have a problem when I use the USB plugs direct however.
The USB hub does use an ac adapter, and all the other devices attached use an ac power plug as well, so I am not sure why I am having power issues.
I thought about plugging one of the two ends of the USB "y" cable into an ac charger (such as powers an iPhone) but the back of my mind says power might travel the wrong way and fry my iMac, so I have been afraid to try so far.
Oh, and the Samsung bluray drive does not have any port to hook up an ac adapter, it only has a mini USB port, and included a y cable with 2 full sized USB plugs on the other end.