Uh....because they look nicer and polished. Less harsh.

Now Steve....You're right! 

Red black and blue complament each other.

Compared to round corners...yes, square is more harsh in a design sense. That's just basic design.

I think it is safe to say that everyone will have their own likes, dislikes, colors and combinations there of and yes even what shapes the frames corners are when putting their desktop together.   There are even some folks that won't step outside of the box, as it were, because the graphics are too busy on most WBs. 

I set my desktop up to please me and so far I have been able to do that very well with all the different skins being uploaded to the WinCustomize Gallary Libraries.  Come to think about it that is what customizing your desktop is all about. 

Apple makes things with rounded corners and everyone copies them because they want to sit at the cool kids table too.

Jon

so they don't poke their eyes out...       

I always try not to be a square when designing a skin

-But I see it over there, and Yes... It do have round corners

I had a rant about this before but I will say it again that I think the whole usability thing is dumb anyway. I theme my gui because I like the way it looks and having skins that are not square or do not have round corners do not take away from the OS usability. I set my screen up to try to be unique and quite honestly I wish there were more skinners that would use their artistic ability to step outside the box and create blinds etc with start menues that did not look like a shoe box. madcat was one who would do that but few else do these days. that's just me though and I know there are many who are content with having shoebox start menues and a long boring line for a taskbar.

I always make mine 'square'. I don't like round corners.

Besides, everyone else does round corners and I like to be different

Here's what I'm using today:

Cause round is the shape of perfection...   see ?

I'm intuit!