I always took it as a given that employees will not get rich off an acquisition, unless the company is a Google or Netscape or Stratus (and even then, only if they were management-level and hired fairly early on). I did the math on my last equity offer (as an employee; not counting cofounder offers): I would've ended up with about $5000 worth of stock in a best-case (~50M) acquisition. My former coworker was an early employee of CCBN, purchased for $40M: he ended up with $3000.

Both founders and employees need to be very aware of the different risk/reward structures for each. I've heard some founders complain about how hard it is to get decent, hardworking help. Well, of course it is - their upside is 1/10th of yours! And their downside is lower as well, since they usually take a market-rate salary. People are less inclined to put in herculean effort if they have no incentive to do so.

For employees, be very cognizant of how much risk the founder has actually eliminated and make sure that fits with the reduced reward. It's really, really hard to build something people want: if they've already done so, they deserve every bit of those outsize founder stakes. But if all they have is an idea and some VC funding, they're asking you to bear many of the same risks, yet leaving you with much less of a reward.

The takeaway, IMHO, is don't hire and don't take VC money until you have product/market fit. That gives your employees a risk & upside profile inline with their equity stakes. It also gives your VCs an acceptable return without them forcing you into taking outlandish risks, eg. going after that pie-in-the-sky market opportunity.