[est31]

Even with 1x preferences, the company might have raised $2 billion but sells for $1 billion because the investors don't want to get any further losses.

The general rule of thumb is that acquisitions are bad for employees, and IPOs are good, especially if the share price is stable for 6 months.

[jaredsohn]

Also for acquisitions, often you'll have to work at the acquiring company for some time to get money from your options. Or might get options in the acquiring company instead (which again are worth nothing until some future possible equity event which hopefully translates into cash).