I don't know if its just my phone, but the usb connection with my PC is very slow. I know it's not mass storage connection but what the hell, it takes ages just to load up thumbnails in the galery folder when I access it thru my PC.
BTW. Its not like the connection is slow, its like if the connection has a very high "ping". Just accessing folder is very slow, but when you finally manage to select something and copy it, it's fast.
Is the connection via USB to PC fast with your phone?