For everyone complaining about the UI and management functionality, realize that you are not the target audience. Head over to www.mobileread.com, look at the Calibre forum and the praise Kovid gets, and you'll see that he's largely catering directly to what his core users want.
It is interesting that Calibre and mobileread are still around, and relatively little changed. I lost interest and moved on once pretty much every commercially-available e-book became available in EPUB format. What's left is a very, very specialized core of enthusiasts.