The below referenced NYTimes article.
Why would anyone want to work for a unicorn? Why bet against the smartest guys in the room. Why are they so smart. Their tax rate is half of yours and mine. They are last money in and first money out. The history of unicorns when they are written will show more fail to increase shareholder value. Good Software is one, so will be Gilt, and there will be many more to follow. When Unicorns history is written it will show that employee shareholders were to big losers to those investing at unicorn valuations with the last in, first out shareholder agreements.
Rules, never buy stock with after tax dollars when you should be asking to purchase, at a nominal price, warrants or other stock like consideration. Make sure you have a cost known as your basis. If you don’t have a basis, a cost you have paid, you will end up with what is called Phantom Income. That is when you have a tax bill and no cash from the event to pay the tax bill.
http://www.nytimes.com/2015/12/27/technology/when-a-unicorn-start-up-stumbles-its-employees-get-hurt.html?hpw&rref=technology&action=click&pgtype=Homepage&module=well-region®ion=bottom-well&WT.nav=bottom-well&_r=0