Stalker0 said:
I think the problem is mounted combat quickly become outdated as you get higher in levels.
There was a reason He-man rode Battle Cat.
As others have mentioned, the mounts can no longer survive the damage from mid to high level encounters. Let's also not forget the problems with moving mounts around in dungeon settings.
If a steed served well, Awakeing Mr Ed might be a good idea. Of course if you "use mount for cover" a lot, he will flee as soon as possible.

Awakening adds 2 HD off the bat and then allows for the critter to take character levels.
The system does need Dire animals and construct mounts costed for higher level mounted combat. When you are twice as tough as your mount, you need to upgrade. Sadly, Wotc rigged nearly all other
Would be cool to ride. animals much slower than horses.
Rear a wild animal
15 + HD of animal
Rear a Wild Animal: To rear an animal means to raise a wild creature from infancy so that it becomes domesticated. A handler can rear as many as three creatures of the same kind at once.
A successfully domesticated animal can be taught tricks at the same time it’s being raised, or it can be taught as a domesticated animal later.
Combat Riding (DC 20): An animal trained to bear a rider into combat knows the tricks attack, come, defend, down, guard, and heel. Training an animal for combat riding takes six weeks. You may also “upgrade” an animal trained for riding to one trained for combat riding by spending three weeks and making a successful DC 20 Handle Animal check. The new general purpose and tricks completely replace the animal’s previous purpose and any tricks it once knew. Warhorses and riding dogs are already trained to bear riders into combat, and they don’t require any additional training for this purpose.
DIRE BOAR
Large Animal
Hit Dice: 7d8+21 (52 hp)
Initiative: +0
Speed: 40 ft. (8 squares)
Armor Class: 15 (–1 size, +6 natural), touch 9, flat-footed 15
Base Attack/Grapple: +5/+17
Attack: Gore +12 melee (1d8+12)
Full Attack: Gore +12 melee (1d8+12)
Space/Reach: 10 ft./5 ft.
Special Attacks: Ferocity
Special Qualities: Low-light vision, scent
Saves: Fort +8, Ref +5, Will +8
Abilities: Str 27, Dex 10, Con 17, Int 2, Wis 13, Cha 8
Skills: Listen +8, Spot +8
Feats: Alertness, Endurance, Iron Will
Environment: Temperate forests
Organization: Solitary or herd (5–8)
Challenge Rating: 4
Treasure: None
Alignment: Always neutral
Advancement: 8–16 HD (Large); 17–21 HD (Huge)
Level Adjustment: —
Dire boars are omnivorous and spend most of their time rooting around, much as ordinary pigs do. They viciously attack anything that approaches them, however.
Dire boars grow up to 12 feet long and weigh as much as 2,000 pounds.
Combat
A dire boar charges its opponent, trying to rip the target open with its tusks.
Ferocity (Ex): A dire boar is such a tenacious combatant that it continues to fight without penalty even while disabled or dying.