I'm offering this opinion just to be a little contrary, buuut..
On a desktop, I don't want most apps using every processor they can find. I'd be much happier if they efficiently used one processor. I'd even be happy if they ate up one processor and stuck there. That way I could run my badly behaved app that eats up only one CPU and do the things I like (surfing perl monks, for example) while the badly behaved app beats up one of my cores in the background.
The problem with encouraging applications to seek out new cores, to boldly go where code has never gone before is the crummy programmers who can't write things that coexist with others are going to go take your whole machine because they can.