Anywho, managing a big ebook collection is challenging. Some people recommend specialized software like Calibre, but I prefer the minimalism of a file manager like xplorer². Sadly most kindle ebook formats (AZW, MOBI, PRC) are encrypted, so you cannot have the usual conveniences like text previews and thumbnails, but there is a plugin that can export thumbnails for some of them (the unlocked ones).
The EPUB format is not restricted to Kindle and is not handled by the aforementioned MobiHandler plugin. I discovered that it is just a renamed ZIP archive. One way to preview an EPUB ebook is to rename it (change its type) to .ZIP, but that's not very sensible. Instead, you can edit the registry to change its type to CompressedFolder, then windows explorer will browse into it. All you need to do is to run this little registry script:
Windows Registry Editor Version 5.00 [HKEY_CLASSES_ROOT\.epub] @="CompressedFolder"
Use any text editor like notepad to save the above registry script in a REG file and then double click on it. If you have an ebook reader installed you can use the Open With context menu. Having said that if you have an ebook reader perhaps you don't need the recommended tweak at all.