Originally Posted by kovidgoyal
About the only criticism of the UI that I'd agree with is that it lacks graphical effects like shading/rounded corners/translucency etc on windows and OS X, which gives it a "outdated" appearance.
That is one that is valid, I think. I am entirely in favour of updating the UI to make it appear more "modern" in appearance, but I completely agree that it should not hinder functionality in any way. I love Calibre, and use it daily. Admittedly, I use no more than 25% of its functionality, but I can usually find the rest when/if I need it. And yes, I might choose a different set of icons, but again, that's a trivial change.
One thought that might answer some critics, and provide some folks with a chance to actually put their efforts where their mouths are, is to enable custom "skins". This could be as minimal as a set of icons, or get into other elements. Yes, it would require a fair amount of developmental effort to enable it, but would take the onus off for future UI changes.
(disclaimer: I am not
a developer, and haven't looked at the Calibre source code. I have no idea how much work it would be to enable custom icons or skins.)