Bitcoin Forum

On most Unix systems, there is an /etc/shadow file that holds hashes of all the users' passwords.  Security auditing and security compromising programs often use this file as input and hash a bunch of password guesses to see if they can find passwords (preimages) to go with the hashes.

Now, for completely unrelated reasons, we've built hardware that does hashes four or five orders of magnitude faster than they were done before.  Have we created a password-guessing security threat that didn't exist previously?  Or are there good reasons why blockchain eruptors etc can't be used that way?

Non applicable at all. Well, slightly, but since miners do 2xSHA256, it's unlikely it will affect anything. And it's only good for SHA256.

that makes me wonder then, what else uses sha256?

I had a hammer that drives nails really good.  Then I bought a nail gun.  Now the hammer is not as useful, but that doesn't mean I'll use it to change the tire on my car.

The ASIC devices are very specific to the Bitcoin mining process.  The only thing they would be good for is any other coin that can be mined with the same process, like NMC.

The life of a piece of Mining hardware today is likely to be less than 6 months, before it cost more to run then it will make.

It isn't just SHA256, it's double-SHA256. Not SHA256(block), but rather SHA256(SHA256(block)). That is the only thing that bitcoin mining ASICs can do.