Good design must be usable; otherwise we'd call it art.
That Facebook redesign for example, while very aesthetically pleasing it looks horrible or confusing to use:
* Search box doesn't look like an input control
* Low contrast for top right nav (how do I change to any other page?)
* Where did my groups and apps go?
* Large pictures, great for mock ups, but it just means more scrolling when 80% of
content I don't care or want to see;
I really don't want to have a picture of a high school friend's baby take up the whole screen
* etc.
They later changed the search box, but I recall at the time their motivation was "we want the title of the page to also be a search field, rather than just a search field". It sort of made sense.
Good design must be usable; otherwise we'd call it art.
That Facebook redesign for example, while very aesthetically pleasing it looks horrible or confusing to use:
It looks nice though.