How does job security in academic untenured soft money positions compare with job security in industry?
I work at a company with a lot of similarity to soft-money academia: research is PI-driven and mostly funded by external contracts and grants.  In the US, there are actually a lot of companies that either wholly or in part operate this way.

In this type of research organization, in some ways there is more security than an academic organization and in other ways less.  Here are the key points as I see it:


More individual job security: In most academic soft-money posts, you are tied primarily to your grants or the grants of the PI that you work for.  There is very little organizational commitment to you as an investigator.  Thus, if your money dries up, there is little or no bridge funding to keep you going as you try to get more money; you just stop getting paid.  In a permanent corporate post, there is a fallback to being assigned as a performer on other people's projects, even perhaps in other departments, and the company is motivated to find such connections because you are still being paid.
Less institutional job security: On the flip side, universities are extremely durable as organizations, and tend to change much more slowly and less dramatically than companies.  A company might be suddenly acquired or change leadership and suddenly all of its policies change radically.  So despite having a position, you might find yourself not wanting it under a new regime---or research itself might be jettisoned, and you along with it.  


The lack of institutional job security, however, is actually less bad than it appears, for anybody with either a healthy research program or who is well-known as a talented contributor.  In practice, what bad institutional change tends to mean is that you end up with a diaspora, in which good people move en masse, either joining other nearby companies with better research cultures or founding their own.  This might happen even if the new "parent company" doesn't have an office in the area---I know of more than one regional branch office that was opened because a group of researchers left Company A and their colleagues at Company B invited them to join, figuring that geography could be worked out one way or another.

In short: from what I see, externally funded research at companies is significantly more stable than soft-money academia, despite the fact that company identity may change over time in various ways.