Post founding, there's this time period where the early employees are expected to work pretty much like founders (long hours, wildly high expectations), but with a greatly reduced salary and the promise of large option grants.
This unfortunately places the employee in a really bad negotiating position with respect to salary increases, etc. as their starting point was so bad. I've been in this spot and a couple years on had to _fight_ just to get a market rate.
1 - Hat tip: Gail Goodman and the long slow SAAS ramp of death - http://businessofsoftware.org/2013/02/gail-goodman-constant-...
In the end they ran out of money and all the employees got laid off, getting nothing.
Here I am though, working for another startup. This one actually makes money, though.