If they are a contractor, mostly yes. If they are an employee, you have payroll tax, tax withholding, etc.

ADDED: And, if you're working full-time for someone as if you were an employee, you may not actually be allowed to be a contractor. See the current Uber discussion going on in California.

"depends". In the UK the employer pays taxes on behalf of the employee, so if you only work for someone(instead of running a company) you never have to file a tax return, everything is calculated and done for you.

It is, so the individual needs to be aware of what taxes apply to them - and especially if you're making bay area money, it's probably a good idea to have an accountant to make sure your tax returns are correct and efficient.