What, no. The problem is that the typical arrangement is that employees must either buy their options (which have been very expensive at Dropbox for past 5 years at least, and thus out of reach and highly risky for most), or forfeit them soon after they leave.

So in practice, employees are shackled to the company until IPO happens.

(Note: some more progressive companies have been combating this dynamic a number of ways -- I don't know if Dropbox is among them)