"Discovering items".... yawn

I found a huge post with LOT'S of suggestions. It could be related to many things...

First step would be to boot into Safe mode and see if the behavior is still happening. If it isn't you know it isn't Windows related but some kind of system driver (e.g. your antivirus even though you have it disabled).
Other suggestions include thumbnails, file permissions, too many files in a folder, etc... just read through the thread and try some things:

Extremely slow file copying / moving / deleting

I've worked around this by moving large folders from the command-line (cmd.exe) instead:

c:\> move c:\stuff\big-folder c:\other-stuff\some-other-folder

This works very quickly for me for dirs under the same drive letter. Also, any explorer window displaying the source or destination dirs updates within a second after the command-line prompt returns.

When selecting and moving multiple items, I use dired-mode (under emacs) which works with similar speed when moving files/dirs within the same drive letter.

I had that same extremely annoying problem, where deleting empty folder would block while "discovering items".

The moment when I killed TSVNCache.exe and/or TGitCache.exe discovering was done and I didn't have that problem anymore. So, not only all that Tortoise stuff asks you to reboot your PC with every update, it also screws explorer badly.