I have a Lenovo y500 laptop (summer 2013). I have a microsoft wireless mobile mouse 3500. Whenever I plug in a USB 3.0 device such as my WD USB 3.0 External HDD or USB 3.0 flashdrive, my wireless mouse starts to lag so bad it's barely useable. It becomes useable when I unplug the USB 3.0 device or just plug it into my USB 2.0 port. My trackpad still works regardless of when I plug in my USB 3.0 devices. Is it just my mouse has a crappy receiver? Should I consider getting a bluetooth 4.0 mouse?
USB ports share a hub meaning each USB port does not offer a direct data connection to the PC / laptop. It seems likely when the USB 3.0 hard drive is plugged into the USB 3.0 port it could be interfering with the other USB ports. It could be a driver issue so you may want to check if there is an update. If that does not work, then you either need to connect the hard drive to the USB 2.0 port or get a bluetooth mouse.