I've had a real hate/gratitude relationship with Calibre. It's a volunteer program, and there's nothing else that covers the ground it does, so I'm glad there's
something. Whenever I actually try to use it, though, it's exasperating. I'm always reminded of
"The Entity" from Southpark (NSFW). No matter what minor task you want to accomplish, Calibre assumes you want it to have total control of every book on your hard drive and are never planning on using any other software (including Windows Explorer) for any related purpose again. It really is like iTunes for ebooks ಠ_ಠ
When you do have more than a few dozen ebooks that you want to get organized with metadata and you're committed to using Calibre to do it, it's mostly great. For anything short of that, though, like just format-shifting files that are already where you want them, the process will be anything but intuitive and you'll likely spend as much time undoing everything you didn't want Calibre to do as actually performing the simple operation you installed it to accomplish.