explorer.exe hogging CPU, slow folder browsing
Run the services control panel (Start => type services.msc and hit enter).
Scroll down to Superfetch. If you find that it is marked "Started", it may be the culprit.
Superfetch is supposed to monitor how you use the computer and cache or otherwise find ways to speed everything up for you.
In my case, stopping the Superfetch service and right clicking on it, choosing Properties, and setting Startup type to Disabled instantly resolved all performance issues.