  We study the effect of a sequential fourth generation on b\to s gamma, B_s
mixing, B\to K^{(*)}\ell^+\ell^-, X_s\ell^+\ell^- and \phi K_S, taking into
account the presence of a new CP phase in quark mixing. We find that the
effects via electromagnetic and strong penguins, such as in b\to s gamma or CP
violation in B\to \phi K_S, are rather mild, but impact via box or Z penguins
is quite significant. Not only can one have much larger than expected B_s
mixing, even if it is measured near the present limit, mixing dependent CP
violation could become maximal. For electroweak penguin modes, the fourth
generation can provide the enhancement that perhaps may be needed, while the
m_{\ell^+\ell^-} dependence of the forward-backward asymmetry in B\to
K^{*}\ell^+\ell^- can further probe for the fourth generation. These effects
can be studied in detail at the B factories and the Tevatron.
