Okay.
I told Nitram to reopen this topic and since he is my slave, he complied.
Now:
The by far biggest issue with horses is the lack of graphics (like my serf previously mentioned.

). As there is no "quick" way of getting the graphics we want, I suggest a temporary work-around. It might seem like a duct-tape fix at first, but really.. should we keep a feature like this (fun for the players, useful, a real money sink) away from the game just because of this? I don't think so. We've had a long track-record with temporary solutions (such as using the "Human" graphic to represent the halflings for.. how long was it? Years?

)
So, before our highly regarded team of artists come up with the necessary graphics for horses, we can simply use a second set of the normal character graphics with a big, fat, neon-green "H" visible underneath them, describing that they are riding on a horse. As the actual graphics are made, we can gradually begin to replace these "temporary" graphics with new ones.
Okay, on to horses.
Some basic theory:
1.0) Horses are a good that the NPC's have a monopoly on.
1.2) Under certain sitiuations, the horses are "consumable goods" meaning, that you can lose your horse should some conditions apply. -> You have to buy a new one (see: 2.1). (Thus the leakage of money out of economy is increased)
1.3) Due to 1.2, the horses are not priced too steeply. The point is that the thing is used and even quite regularly. So the price of a horse could be, 50-100% that of an "Okay" armor. 10-20 Silver coins is what I had on my mind. Max. (If they are too expensive, people won't use them when they risk loosing them..)
1.4) Horses are useful for players (and against other players). This encourages their use. If the players can feel the benefits, and especially if they know that using a horse gives benefits to other players.. they will purchase and use them.
1.5) Horses are only usable in the basic level of the map. No using of horses underground, or "upper floors" (due to the advantages logically not really being useful there).
Horses a battle:
2.0) You cannot unmount a horse while in combat (Or you can, but the 2.1 rule applies for some time after the combat..

)
2.1) 2.0 is due to the fact that when you mount a horse and die, there is X-change (high, ~90%) of losing the horse. If the horse exists as an icon in inventory (see: 5.2) then the the player would have a smaller (25-50%) chance of losing it in the case he dies while not mounting the horse.
Okay, the advantages of horses:
3.1) Horses reduce the amount of stamina-loss you experience due to walking around by 75%
3.2) Horses make you move around a bit faster (not so much on the normal ground, in order to keep the distances as "long".. but they could have better speed over "bad" terrain)
3.3) Horses give you (noticeably) more hitpoints (as such a large animal is likely to absorb some hits that were ment for you)
3.4) You hit with (noticeably) more damage and accuracy from above. (Perception is increased, strenght is increased, dex is increased)
3.5) 3.4 Advantages are bigger against unmounted opponents.
Disadvantages of horses:
4.0) You make a bigger target for archers. Increased chance to hit and damage for throwing/arrow weapons.
4.1) As you can see, the actual disadvantages are (very) few in my idea.. just for the sake of encouraging people to *spend* money on these.
Problems I could come up with and possible solutions:
5.1) How/where the horse is mountable?
5.2) Where it is while you are not riding it? (Inventory a la WoW would be the handiest, I suppose.. but that could lead into "cheesy" sitiuations where you just magically hop on the horse out of the blue..)
5.3) Is there any other way of doing that than the inventory?
5.4) One possibility would be "horse only" depots (the medieval bicycle-rack

) where the horse would have to be 'stored' while not using. That would lead to funny sitiuations in the wilderness though, for the lacking ability to unmount.
Misc:
6.0) Lizards, Dwarves, Gnomes, Halflings and Faeries have less advantages with horses due to physical reasons alone.
6.1) The degree of these could vary, but I think lizards should finally get some stick instead of carrots. (Eg, I would possibly go as far as to forbid Lizzies from riding completely. The horses would probably agree.)
6.2) Perhaps the smaller races should be restricted to a weaker (and cheaper) version (called surprisingly "pony") which would be available for the others as well?
Does this sound better, my serf?