Among the data on affected systems: payroll records, prisoner information, official e-mail. Just the sorts of things network administration is supposed to protect.
San Francisco is hardly a small or midsize business (what government body is?) but the lessons in this still-evolving situation are clear, and are as applicable to you as to city government or big business network.
The security -- not to mention the basic availability -- of your network and the information it contains is no better (or worse) than your sysadmin's diligence, skills (supported by necessary resources, of course) -- and integrity (or mental stability.)
As we've said before, and frequently, small and midsize businesses have an advantage here: it's far easier for you to know the members of your team well than its for a large enterprise or, for that matter, big city bureaucracy.
But that's begging the question, really -- I feel fairly confident that as the San Francisco lockout story develops we'll hear plenty of testimonials about what a good, normal guy the now-jailed systems administrator seemed to be.
Besides, let's assume that you never have to face system sabotage by an employee (and probably you won't) -- what happens if your administrator is unexpectedly incapacitated or worse? How much control resides only in that admin's head? How much access would you have to the administrative tools you or your admin's successor would need?
Or suppose you outsource your administration and maintenance: What happens if your vendor goes under? For that matter, to return to the disgruntled side of the question, how confident are you of your vendors' staff -- and what guarantees and assurances have they provided you in writing of the same?
Probably no one saw the San Francisco situation coming: which doesn't mean that it wouldn't happen (it has) and sure doesn't mean that this sort of thing couldn't happen (it did.)
You can see how quickly this one becomes a slippery slope -- in addition to the obvious problems of widely distributing top-level access (creating as many or more problems than you solve) there's also the endless question of who controls the controllers who controls the controllers who...
A slippery slope indeed -- one that runs uphill.