I'm blogging this mainly because I spent hours trying to export my highlights/notes from an ARC (Advanced Reader's Copy) of Juma's Rain. The only thing you can find online is how to export notes from a Kindle reader (and usually a store-bought book) to a PC but not from a PC to... well, PC.
So basically I had two problems:
1. I was reading an ARC, therefore it was not an Amazon book (at least not yet - it releases next week), and therefore did not appear in my online highlights file.
2. I made my notes on the Kindle for PC, therefore in no universe could I "connect my Kindle to the PC via USB and export the myclippings.txt file." Heck I couldn't even find a myclippings file.
Okay, so the trick is this: look for the .mbp file.
I saw this file earlier and ignored it, and when I looked for it again, it wasn't viewable anywhere. Until I had the bright idea to import files into Calibre (I was trying to see if I copied the .mobi file into Calibre, would I see the notes? The answer is: no). It was then that the .mbp file appeared in the import folder, I imported it, and then opened it with notepad.
Note: I played around with the settings in my folders again and now the .mbp files are viewable. I'm not sure what I did; but I must have accidentally hidden the file type. But well, if you can't find them, rest assured, they are there - you just need Calibre to make them visible.
But anyway, if you want to export your notes/highlights from Kindle for PC and all you get are myclippings files, remember this: MBP files.
(Oh the things you can find once you know what to look for)