It will most likely slow it down enough that you can't use Ready Boost. Vista judges whether a drive can do ready boost by it's random access times. So putting it in the hub will likely increase your latencies, and hurt your random access times.
“What the hell did you expect? Leave Vista under the pillow and the OS fairy would make it Win7?” -El Fiendo
“And Bring Mailman back god damnit, he is the Eric Cartman of TPU” -MRCL