Conclusions
1. Clusters are a potential tool of “precision cosmology”:
~200 from SZE (0<z<3)  or ~2000 from X-rays (0<z<1).
2. Using shape and normalization of dN/dz, complementary to
other probes (CMB, SNe, Galaxies):       W0 vs w plane.
3. Few percent statistical accuracy can be achieved on W0, w
more work needed on systematics (cluster evolution).