
The scope of my job and the quality of my coworkers.
Dropbox has recently shown solid commitment to improving its middle management, both through training of existing staff and by bringing in experienced managers from larger companies.
Not only is the equity publicly tradable now, but salary is also slightly high both in comparison to other offers and as a percentage of total comp.
There are always opportunities to take on ownership of new areas, and since the company is growing, people are glad for the chance to share the load, rather than territorial and defensive of "their" space.