Now Kyhokie, that is not accurate. Like bettas and cichlids, crayfish all have their own personalities and not all are ruthless night stalkers. I'd say a dwarf cray with a pleco would be fine, but a full size cray fish even an alleni could potentially injure or kill the fish. I do not suggest putting a Hammers Blue Lobster - What even in the He%# that is in a 36gal with the bottom dweller.
Here is the education part - First, several breeds of crayfish are much less aggressive than others. I have a large number or Marmorkribs, marble, crayfish. All of mine live with fish. I have several individuals that live in tanks with corys and never bother them. These are just different individuals. I have some of their siblings who would attempt to eat the corys until successful, so they live in deep tanks with fast moving fish. It really just depends on the individual and availability of food. I find those that are fed, not scavengering, don't bother the fish. Crayfish are shy and lazy by nature so an easy meal is a good meal. Additionally, some large crayfish such as Cherax have such large claws they can't move fast enought to catch a fish if their life depended on it. They look scary, but they are not much in the threat department. Clarkii are the most common Blue or White crayfish and are a very aggressive breed. They are not really good community tank candidates and don't even tolerate each other.
Next, there are no freshwater lobsters! These crayfish have names and the pet industry should use them so people know what they are getting. A Blue Lobster can be anything from a Alleni to a Cherax Destructor or Red Claw Cherax almost 12" in size. If they can't tell you what it is don't buy it. Also, crayfish really need to be fed. They are great clean up guys in the tank, but need a dedicated food source. Mine eat peas and cut up fish. Marble crayfish turn blue when you feed them real fish.