Intriguing article on why we love rounded corners: http://www.basement.org/archives/2005/11/why_do_we_love_rounded_corners.html

Interesting read, but I disagree with the hypothesis given for why we (currently) love rounded corners.

I would guess, and history will prove me right or not, that the primary reason we love rounded corners is nothing more substantial than temporary differentiation.

On the web, for instance, it remains true that rounded corners are a minor barrier-to-entry of "cool" website designs (I had to waste an hour of my life making those silly rounded corners on this blog in Photoshop, and then playing with CSS and tables so they worked properly in the major browsers), so they do, to a very small degree, differentiate a design. By the same token, there was a time when everyone thought that animated cursors, background music, and intro flash graphics were a great thing because each of them required a bit of knowledge and effort. It certainly isn't a given that such preferences remain.

Earlier I said that history would prove me right or not, but really there is plenty of historical evidence already demonstrating this recursion of aesthetic preferences: Design trends have tended towards extreme roundedness ("organic"), back to squared and sharp ("modern"), then back to rounded, then back to squared and sharp, in an endless cycle. You can look in virtually every market (cars given as examples here) where this cycle took place, with each design philosophy welcomed as interesting and fresh looking, but quickly evolving to old and dated as everyone followed suit.

Soon enough everything old is new again, and it repeats ad nauseam.

I would predict that as more and more blog templates incorporate rounded corners, and CSS3 makes them absolutely pedestrian, rounded corners will become the domain of the amateur johnny-come-lately. At that point we'll be talking about our next-generation, ultra-modern square corners.