I'm pretty interested in SSX3's upgrade to the whole friend/enemy thing that Tricky had going, too. If you kept knocking someone down, they eventually began to hate you, and go out of their way to make your life hell. They'd diss you before the race and so on. While your friends would sometimes go out of their way to knock down your enemies in the race (Never really worked.... DAMN YOU, KAORI!)
A small little novelty feature, but it was pretty cool.