I have read in various places that mushrooms in lawns are an indication of woody compostable material that is being eaten by the mushrooms and that the by-product of this process will be additional nutrients for the lawn.
Can this same process be used in a vegetable garden? @bstpierre mentioned that mushrooms would compete well against the vegetable plants for the nitrogen in the soil in this question. But if there is a lot of uncomposted material from the previous season (stems, roots, leaves, etc) lying on top of the garden (left there as mulch/soil amendment) can a balance be struck with mushrooms mostly feeding on the mulch and the plants eating the nitrogen in the soil? What species of mushrooms would be good for this? It would be nice if the mushrooms were edible.