  We study solutions of Einstein gravity coupled to a positive cosmological
constant and matter, which are asymptotically de Sitter and homogeneous.
Regarded as perturbations of de Sitter space, a theorem of Gao and Wald implies
that generically these solutions are `tall,' meaning that the perturbed
universe lives through enough conformal time for an entire spherical Cauchy
surface to enter any observer's past light cone. Such observers will realize
that their universe is spatially compact. An interesting fact, which we
demonstrate with an explicit example, is that this Cauchy surface can have
arbitrarily large volume for fixed asymptotically de Sitter behavior. Our main
focus is on the implications of tall universes for the proposed dS/CFT
correspondence. Particular attention is given to the associated renormalization
group flows, leading to a more general de Sitter `c-theorem.' We find, as
expected, that a contracting phase always represents a flow towards the
infrared, while an expanding phase represents a `reverse' flow towards the
ultraviolet. We also discuss the conformal diagrams for various classes of
homogeneous flows.
