My initial impression of this piece of software is good. If I was to draw a correlation, I'd say that Calibre is like music management software, except for ebooks of all formats.

If you have tons of pdf/mobie/etc ebooks neatly organized into their respective folders or if you have them all in one disorganized folder or all over your harddrive, then this software is for you. You can scan folders, subfolder, even the entire hdd and Calibre will add them it's own Calibre Ebook folder. This creates a copy of the already existing ebook. I'm not sure if you can just add the ebook to Calibre without making a copy though.

In addition, you can edit the meta data of the ebook, just like the ID3 tag of an mp3 file. And if you are on the go all the time, then Calibre can convert the ebook into a format that is compatible for you portable device, such the iPhone, Android, etc.

I haven't looked into all of it's features, but this is definitely worth installing and trying out.

I haven't looked into or tried any eBook management software before, so if you know something better let me know.