As a note for everyone suggesting using exotic mounts--think about this. I did the math on how much mounts of any given level should be able to carry based on DMG 184. If a 300 lb dragonborn runs around naked, it needs something with 24 strength to carry it around, i.e. a level 16 quadrupedal brute. Btb mount rules mean Dragonborn have to walk until they're ready to leave the material world and shake the foundations of the universe. I rest my case. ;-) Proposed house rule--when mounted, a character is assumed to be carrying all the gear on the mount. The mount shares whatever encumbrance category the rider has. Unrealistic? Yes, it means a halfling wizard's horse carries far less than a dragonborn fighter. But, it's superior, imo, because it takes away all of the hidden punishments for choices the PCs don't fully understand at character creation.