As the newb on these forums, I'd like to contribute to a further elaboration of usage?!
Let's pretend that John writes an article about CarWax on his blog. He explains the pluses and minues, etc. the brands, makes, techniques, etc.
Mike, who also has a blog, reads the article on Johns blog. So Mike writes about his new car, and how he loves to pamper and baby it with CarWax. Mike writes his own blog article 'inspired' by the one originally written by John. Mike is kind enough to use the trackback URL provided by Johns blog.
On Johns blog, he receives the PING from Mikes blog associated with his CarWax entry.
He is delighted (quite ecstatic) that someone sent a trackback ping. He is glad someone found his article useful. Now, whenever a visitor to Johns blog reads the CarWax entry, they come across the comments section, and read that Mike uses a similar but different style and method to waxing his 2005 Hyundai Accent.
Now, thanks to pings and trackbacks, Mike has a new visitor that he would have never had.
... fast forward X amount of months later ...
Mary, Josh, EvilRedEye, WikiWilly, and RobitussinRobbie all have written a blog entry of their own discussing the DOs and DONTs of carwaxing, washing, detailing, etc.
Thanks to their blogs, trackbacks, and pings, John & Mike are in the higher echelons of the 'food chain of the animal kingdom' cause they get all the traffic based on ONE blog entry.
<< i hope i was able to explain in a real-world type scenario how this works. >>