The DX record for communications at optical frequencies is phenomenal these days. There is a growing interest in communications over non line of sight paths (NLOS) using cloud-bounce or clear air scattering. To my knowledge, in recent times experiments are (or are about to start) by F1AVY, VK4EBP , VE7SL and G3XBM (when fit again). I am sure there are others too. Weak signal modes certainly help. I used QRSS3 over an 8.5km NLOS path, but much further has been achieved.
See http://en.wikipedia.org/wiki/Non-line-of-sight_propagation .
A couple of useful optical Yahoo groups are:
Australian Optical DX https://groups.yahoo.com/neo/groups/Optical_DX/info
UK Nanowaves https://groups.yahoo.com/neo/groups/UKNanowaves/info