Was having some wretched file sharing speed issues between 2 Win7 Pro machines. Disabling MSSE real-time scanning didn't fix it. Control Panel -- Network and Sharing -- Advanced -- "Use users and passwords" (instead of "Let Windows manage security") didn't fix it.

What did fix it was: right-clicking the wired-connection icon in the task tray -- "Open Network and Sharing Center" -- Active Networks / Local Area Connection link -- Properties -- adapter settings - disable "Ethernet@WireSpeed" and "Large Send Offload" options. Pow, full 100megabit-per-second speeds for both Win file sharing and MySQL / SQLyog database copying.