I updated my Win7 PC to Win10 a while ago, no problems. I also have the same SolidWorks license installed/activated on my home PC, per the EULA. I just installed the Win10 Anniversary Update today (direct from Microsoft's website, as opposed to Windows Update in settings) and had an issue with the activations. When the Windows update finished, SolidWorks treated it as if it were a new installation and asked to reactivate, but failed due to too many activations.
Not a huge problem, as I was able to call my VAR and get them to deactivate the unused instance, but I thought I could save some people some time/headaches here. When I update my home PC, I'm going to deactivate SolidWorks first then reactivate after the update.