Just upgraded to 5.6 this morning to check out the new hotness in it. I noticed, though, that no node thumbnails are rendering (even after right clicking and doing "Compute node thumbnails"). I can double click on the nodes and see their contents in the 2d Preview window but in the graph I get nothing.
Also, my 3d View has no geometry in it. I've tried hitting "F" to Focus the camera, and I've tried switching geometry to different things, but no luck so far.