Tech workers are warning each other about the dangers of working at Silicon Valley's hottest companies.

There are now 140 so-called unicorns, privately-held companies valued at $1 billion or more. If those valuations crash, it's the employees who would likely lose out -- not the executives or investors.

The conversation picked up steam after a story in the New York Times about the unraveling of Good Technology. Not long ago, the company was said to be worth $1.1 billion. But then it sold to BlackBerry for just $425 million. The workers ended up with stock worth just pennies.

It's a cautionary tale for all buzzy startups. "Unless the company gets lucky, employees lose," billionaire investor Mark Cuban said on Twitter.

On Hacker News, a tech news and discussion platform, more than 250 comments rolled in, reading as warning flags to those looking to work at a startup.

On salary versus options: "Take it easy on the option grants."

One issue was that employees feel they are taking slightly lower salaries in exchange for stock options. That works out well if your company has a big IPO or gets bought at a premium price. But for every Facebook, there are many busts.

"I've seen countless friends get burned in various ways believing they would be getting rich soon," wrote nemo44x.

One friend in particular, nemo44x writes, chose to stay at a company that offered him stock options instead of a raise in cash. "Did it not ring a bell that a company that can't give cash but can instead offer compensation out of thin air in the form of options is in trouble?"

On what happens to your options when you leave

Another concern discussed was what happens to stock options when you leave the company.

Employees typically have 90 days to exercise stock options. That can be okay if you cash out right away. But there's a lot of risk if you lay out cash and hold the stock.

" Don't pay taxes or exercise options early to maximize your gains at an eventual exit. It makes no sense - keep the optionality," said tomasien.

On the problem with those mega-rounds of fundraising and billion-dollar valuations

Every week brings new headlines of startups raising more money at high valuations. What many don't realize is that the investors have negotiated clauses make it hard for them to lose money, even if valuations crash.

"As a common stock holder, you should know that you'll be the last one paid, if at all, because few companies can meet unicorn expectations," said seanconaty.

On the boss: "There are tons of stories of completely incompetent founders."

Many agreed that you need to trust the founding team of a startup.

"There are tons of stories of completely incompetent and/or corrupt founders literally locking the door on employees," wrote pc86.

One commenter, throwaway1223, added: "[It's] a much better career move for non-founders to work for large established companies."