That's right, the BSA are basically toothless...
You can just fob them off if they start pestering you. In my experience they have always been most polite.
However, FAST are the ones to worry about.
I have seen circumstances involving small businesses where FAST have obtained a search warrant from a court in order to carry out a software audit, and they are assisted by the police.
They will be waiting at your office first thing on a Monday morning, and they will look closely at all of your computers. If there's no proof of a license to use any software that concerns them (e.g. MS, Adobe) then they can confiscate computers as evidence. The directors of the business will end up in court.
There is a fairly good get-out, though. If the business can show 'due diligence' to sorting out any licensing issues, they will probably be let off with a slap on the wrist and maybe a small fine. A nice policy that says something like "we intend to buy a new computer every month to replace those in use, and we will ensure that new computers are only be installed with fully-licensed software" goes a long way in these kind of circumstances.