[pokeymcsnatch]

I'll bite I guess. I use Calibre pretty regularly. I think a general way to put it is that it's not for "casuals". To understand a lot of the functionality outside of the basic inventory management stuff, you have to be a little bit of an enthusiast. For some examples: You have to know about different ereaders and their formats and how they differ, the differences between metadata sources, and dozens and dozens of configuration options if you're trying to convert a book to work well on your device.

Also, there's definitely something "off" when it comes to using it intuitively. I have to devote a lot of brain power to searching for functionality AND trying to comprehend exactly how those pieces of functionality are going to affect my library data.

Maybe it's too powerful of a tool up front or something. It could benefit from a "basic view" maybe?

None of these are complaints from me, I'm a happy user. I'll just echo some other commenters in wishing for a more robust network interface (whether that's just an API, or a more hashed out front end). I'd like to easily share my library with people or just other devices while on-the-go, and Calibre has all the device formatting functionality built-in.