  We revisit Type IIB supergravity backgrounds with null and spacelike
singularities with natural gauge theory duals proposed in {\tt hep-th/0602107}
and {\tt hep-th/0610053}. We show that for these backgrounds there are always
choices of the boundaries of these deformed $AdS_5 \times S^5$ space-times,
such that the dual gauge theories live on {\it flat} metrics and have
space-time dependent couplings. We present a new time dependent solution of
this kind where the effective string coupling is always bounded and vanishes at
a spacelike singularity in the bulk, and the space-time becomes $AdS_5 \times
S^5$ at early and late times. The holographic energy momentum tensor calculated
with a choice of flat boundary is shown to vanish for null backgrounds and to
be generically non-zero for time dependent backgrounds.
