Does dual core help transfer speeds? I read a review of a dual core mobile recently and the reviewer was of the opinion that dual core processor helped the usb transfer speeds.

This doesn't seem to make much sense to me. When the phone is plugged in then it is usually not busy. That is if the processor is even involved in the transfer at all. 

Can anyone post any experience with usb transfers on dual core devices?
That definitely doesn't make sense.  Unless they somehow turned off one core (probably impossible without serious development effort) and compared the transfer rate to when both cores were on, you can't draw that conclusion.  One phone might have a different transfer rate that another, but it has nothing to do with whether one phone has a dual-core processor or not.  The speed of the internal memory or SD card and the filesystem are the most important factors, and possibly the efficiency of the storage-handling code. All three can vary between devices.