  Theories that spontaneously break Lorentz invariance also violate
diffeomorphism symmetries, implying the existence of extra degrees of freedom
and modifications of gravity. In the minimal model (``ghost condensation'')
with only a single extra degree of freedom at low energies, the scale of
Lorentz violation cannot be larger than about M ~ 100GeV due to an infrared
instability in the gravity sector. We show that Lorentz symmetry can be broken
at much higher scales in a non-minimal theory with additional degrees of
freedom, in particular if Lorentz symmetry is broken by the vacuum expectation
value of a vector field. This theory can be constructed by gauging ghost
condensation, giving a systematic effective field theory description that
allows us to estimate the size of all physical effects. We show that nonlinear
effects become important for gravitational fields with strength \sqrt{\Phi} >
g, where g is the gauge coupling, and we argue that the nonlinear dynamics is
free from singularities. We then analyze the phenomenology of the model,
including nonlinear dynamics and velocity-dependent effects. The strongest
bounds on the gravitational sector come from either black hole accretion or
direction-dependent gravitational forces, and imply that the scale of
spontaneous Lorentz breaking is M < Min(10^{12}GeV, g^2 10^{15}GeV). If the
Lorentz breaking sector couples directly to matter, there is a spin-dependent
inverse-square law force, which has a different angular dependence from the
force mediated by the ghost condensate, providing a distinctive signature for
this class of models.
