In this informal talk I will return to an old topic, quantum spin fluctuations and long range magnetic order in two dimensional lattices, with some new twists. I will consider nearest neighbor antiferromagnetic Heisenberg models and the focus will be on the effects due to lattice structure. I will mention some effects of increasing disorder and/or complexity - as exemplified by quasicrystals, which can be thought of as having an infinitely large unit cell- and propose a mechanism for a novel Casimir-type effect.