Seems DrZhark (maker of the Mo' Creatures horsey goodness [and other new mobs which aren't as cool as pegasi]) has made a mod that lets you tame the regular animals (cow, pig sheep, chicken), and a shepherd's crook so you can lead them around. (not working (yet?) with the Mo' Creatures animals though)
cows give manure, which can be used to make plant seeds, so you can plant mushrooms, pumpkins, flowers...
[MOD] Farmcraft v1.0.2 - MC Beta 1.2_02 - Minecraft Forums
... also.... he's working on adding a shark to Mo' Creatures on Sat....
The sharks will sense you in the water from 32 blocks away. They won't attack in peaceful, and they spawn in any body of water that is at least 2 blocks deep and around 6-8 blocks wide/deep. I've seen them spawning in small pools in my tests. I'm still working on what they drop.
Oh and they will attack anything that goes in the water, including monsters/animals/players