Still. Calibre IS very slow. I dpn't believe I have any other program on my computer that is as demanding on my computer, as Calibre is.
I tried just starting and closing some "heavy weight" programs, and monitored CPU usage. OpenOffice Writer, Firefox and The Gimp all seem very modest in CPU-usage, when starting, compared to Calibre.
I suspect this is because Calibre relies to a large extent on code written in Python. While this means that development can progress at a close to neck breaking speed, it also means that the performance does suffer.
I can live with that. I don't mind waiting a few seconds longer for Calibre, than I wait for other programs. But others may become surprised, annoyed and confused when they discover that Calibre is the worst CPU-hog they use.