One of the more vicious characters that I've witnessed is a fighter/wizard/cavalier who used a leadership feat to get a dragon mount (in this case, a juvenile silver dragon).
He's a one-trick pony, but that one trick -- True Strike + Full Power attack + Deadly charge -- is really nasty; his damage easily clears 100 points -- and he winds up about 300 feet away from whoever got impaled, since the dragon usually casts Expeditious Retreat on herself.
Full mounted attack is an irrelevant ability, since doing a single spirited charge is just as good (or better) than attempting 3 to 4 melee attacks against the target.
The key thing is that the knight in question has that dragon, though -- his damage capacity is much higher, but defensively, the mount's harder to kill than he is.
