While trying to use the new cycles volumetric rending features to create crepuscular rays (with the intention of updating my answer here), I have found this to be a little trickier than I anticipated.
When I create a basic setup with a spot lamp (sun lamps don't seem to work, not sure if that is a result of their one directional nature or what..) and a world material like this:
Which gives me this (500 samples):
The problems with this that make me think that I'm missing something (aside from the rendertime and noise, which I understand to be a part of using bleeding edge new features) are:
The background shader/sky texture isn't visible at all (volume is too dense?)
The lamp needed to be set to
50000strength (this is of course dependent on the distance from the camera, but the kinds of strengths required to get some nice defined rays will blow everything out if volumes are disabled)
I can't seem to get a straight render (no compositing tricks) to look anything remotely like the pretty image in the release notes:
Is this just how it works?
Or is there some trick I have missed (not counting compositing/renderlayer tricks)?