Today in my raised beds I noticed a few patches of mushrooms breaking through the 1" or so of wood chip mulch (mixed birch, oak, and maple) I laid down last fall. After much googling, I'm fairly certain they're some kind of Amanita (though I'm really not sure which). Normally, I'd just let them be, but my dogs are young, energetic, and not so bright. If they ever decided to eat one, I couldn't stop them if they were right next to me (they're that quick and usually determined to do the worst possible thing whenever they have the opportunity, probably because they're never allowed out of their fenced-in run or off-leash). So the mushrooms will be removed posthaste.

So: How beneficial are these mushrooms to my soil? I'm thinking it's probably best to let them do their thing and just remove fruiting bodies as they appear. I would assume any fungal activity is good activity, but I just don't know enough about different species and their roles in an ecosystem; I'm hoping they're not like the fungal equivalent of crabgrass. If all the mycelia are any indication, the entire batch of wood chips was thoroughly inoculated and pretty much all of the vegetable and flower beds are now potential death traps for idiot dogs for however long the mushrooms are flushing (in flush? not sure of the proper terminology because I'm a noob). I don't relish the idea of removing and quarantining all the affected material, but if it's not providing any real benefit and posing a(n admittedly remote) hazard, then I'll just get rid of it and go back to using leaf mulch.

And another tangential question: How worried should I be about the shiitake logs I plugged last spring? They're about 20' away from the closest affected area. Would it be better safe than sorry to move them farther away, or is that closing the barn doors after the horse is out?

Amanitas are the classic fairy tale mushroom- red with spots, though I've seen ones that are more orange than red, and some with very few spots.
They can appear seeminglly out of nowhere and be fully "flushed" within two-three days.

I've never seen any of my dogs show the slightest interest in any mushrooms, including the amanitas that come up occasionally around my property.
(But I have a couple of acres for them to roam on, and plenty of other things to keep them occupied. )

Having said that, Amanitas are attractive to some dogs as they have a 'fishy" odor:

http://www.namyco.org/mushroom_poisonings_in_dogs_an.php

I would pull the fruits and not worry so much about the hyphae since they tend to chemically change non-available (to plants) minerals into chelates that the plants can take up and use easily.

The thing to remember about amanita mushrooms is that this group includes "death cap" (Fly Agaric) and others in the group are psychoactive (hallucinogenic) species.
Almost all of the amanita family are considered poisonous (a few are good eaters but unless you have absolute knowledge best to avoid all of them to be safe).

here are some links you might want.
identify poisonous mushrooms
The Death Cap
Amanitas
Fly-Agaric

Thanks for the responses! These look like Death Caps (coloration, gills, cap shape, right on down the checklist), but the spring flush had me confused. The only species of Aminanita I found in my searches that has a spring flush was one of the Destroying Angel types, but A. verna is European (and also pure white in coloration, rather than the brownish/ tan of the Death Cap). It could be some species of Volvariella, but some (though, annoyingly, not every single one I examined) have a visible annulus, which I read Volvariella don't have. As a complete amateur, I think (in this case) it's safest to assume they're the worst kind until I know more about the ins and outs of mycology.

I'm still a little concerned about the shiitake logs but I gather that, if they colonized properly, they should be fine no matter where they are, though maybe not as productive if they have to fight off something else trying to colonize their logs. I guess it all comes down to how overly-cautious I want to be.

Shitake are hardy when it come to withstanding an assault by other varieties.
If you have established logs, then you don't have much to worry about.
The issues come from freshly inoculated logs where the hyphae have not filled in, in those instances another species might be able to gain a foot hold.
Even then the odds are that the shitake spawn will overwhelm the intruder.

I've noticed on our land that the lion's mane does the same thing, in fact in one downed tree we have a 5 foot section that only supports lion mane, then at the very distinct demarcation line, there are turkey tails on one side and jew's ear on the other.

I agree with your assessment of leave the unknown alone. I have been around mycologists most of my adult life and studied the discipline but I in no way consider myself knowing enough to be certain about every mushroom I can encounter on our land.
I still have around 10 species to fully and rightly identify in the immediate 3 acres around our home and I still have 12 - 15 acres or more to go after that. Since we live on the ridge of our hill, we have at least 7 microclimates from one end to the other both up and down hill (North South).
If you go East West each microclimate seems to remain rather stable along their N/S lay lines.