I use this and transfer speeds are around 5-6MB/s. That's because both the hard drive and Ethernet share the USB bus.
And it's completely fine, took around 6 hours to backup 90GB from my MacBook Air.
It is 357GB total that it is backing up that will take 18 hours. :)
oh, you'r right, it's my mistake
laptop backup is done over wifi right ? wouldn't that be the limiting factor ?