I am thinking of growing mushrooms too. I get the impression it's not as straight forward as I originally thought although I have yet to really research the issue.
My original plan was that once DH has mowed the lawn for the last time this year I will load the entire compost heap into a series of daleks, pop a load of well rotted manure from next door on top and then just sew a load of mushroom spawn into the manure and wait and see what happens.
However, I think I may end up buying ready spawned mushroom compost instead as there seems to be difficulties getting it all going.
I'll keep you posted.
Susanna