How high a character jumps depends on the weight, energy, and strength (of the leg, being \'very\' strong in the arms will just allow you to jump with your hands if that\'s possible) of the character that is jumping. Making it a purely race related skill would not be the best of ideas, n my opinion, because there are a few \'odd\' creatures in every breed, and just because someone wants their character to be a Kran simply makes jumping harder to learn. I believe that race only makes the jumping skill easier or harder to use.
As for jumping itself, it is a good idea. If a stamina bar is put into the game, then the higher you jump, the more stamina you use up. Learning how to jump really high should be hard, but as for learning how to jump high is another matter. Anyway, perhaps there can be a spell that allows you to jump higher than normal. You may say that levitation is better, but the \'jumping spell\' can be easier to learn how to cast than leviating yourself, and you can take a quick peek inside a building to see what\'s inside, and you willl either continue going up quickly, or fall to the ground. This is similar to Rageburst\'s idea on potiong drinking and spells, I think.
There could be a penalty for not landing \"correctly\" on the ground. I mean, not crashing into the ground headfirst or something similar. Like someone (I\'m not too sure who) before me said, hit points could be taken away, but perhaps items can be damaged and the character could suffer an instant death.
Finally, if your\'e actually still reading this, you can grab on to ledges of buildings while jumping and hang there. I\'m not sure if someone already said this before me, but I\'m kind of lazy, seeing as it is quite an effort for my eyes to go around and around and around the monitor...