Responding to Jay Cross:
"(No one becomes passionate over something they suck at.)"
Empirically, this is not true. The world is full of people who are passionate about things they suck at. My passion for darts is probably a good example, though there are many people out there who are even more passionate about darts who I can defat pretty handily every time.
How many bad watercolours have we seen? Poorly written science fiction stories? Flickr sites filled with poorly framed and out of focus photographs? People with a 20 handicap in golf?
I think that it's true that you cannot excel at something without passion (though I wonder sometimes about effortless genius), so if you do see excellence you probably see passion. But the converse is not true; if you see passion, you may or may not see excellence.
Still. The important thing is the passion. And, interestingly, when people have passion for something, and are always trying to be better, it does not matter whether the outcome is some arbitrary definition of excellent, or simply the person's best.