Fast-Spinning Planets

[Nick]

What would happen to a planet about the size of Earth, with no natural satellites, if it were to (for no particular reason) start gaining a large amount of angular momentum? At what point would it begin to fly apart? What other effects would happen to it?

And what about bigger planets? Say, a planet like Jupiter?

[eburacum45]

If a planet acquired a lot of angular momentum, the gravity at the equator would decrease and it would probably become more oblate. Most planets are largely fluid inside, or are capable of plastic flow of some sort; Saturn is the most oblate large planet, although 2003 EL61 is even more oblate.
http://en.wikipedia.org/wiki/2003_EL61

If you continue to increase the spin rate and angular momentum, the gravity at the equator will become effectively zero; as far as I can figure that is when it starts to fall apart.

[Hamiltonian]

Some discussion of this on an old thread.