Do I have to pay tax on money given as a gift?

Really depends on who is giving you the gift; for example, wife gifts husband $100,000 cash gift there will not be taxed on the $100,000 cash but income earned from the wife could be subjected to the taxes, also If you get from your employer any amount of cash is taxable.

Similar question, but a bit more complicated.

My boss' company was acquired by another company. He has agreed to pay me a percentage of the total earn out. This is not income, or a bonus, it is simply a boss being a nice guy and profit sharing. Can this be considered gift money?