"Let me check that file for you."

That's Windows Explorer building a thumbnail, your antivirus checking it out along the way and other protection software such as Spybot checking it again.

I didn't even get to how copies slow to a crawl after some thousands files in a folder.

If you want to discuss this, more details but a nod to ROADKIL's UNSTOPPABLE COPIER since it bypasses some of the nutty Windows Explorer nuttiness.