5 million particles, grid resolution 250, 80 simplified children per particle. used 6 gigs/frame, about 8min/frame on i7-920.
I can`t say much about it, except this: http://www.youtube.com/watch?v=Txnf4s7eWs0 
With 256 gigs ram, 1000 cores, some smoke/dust, Blender might be able to do it.
Maybe I’ll try some thing with a little more content/context rather than a simple splash test, to see how far I can push it.
Meh !
See here !
I was reminded of this video http://www.youtube.com/watch?v=ZoZ0ZAzr6eg 
I guess I don’t get it. Where does the sand go to? Shouldn’t it remain?
Yeah, the sand needs more friction.