I wouldn't think of a high yield savings account as a source of passive income but your savings should be getting something (less like Seinfeld syndication residuals and more like a commercial jingle residuals!). It won't make you rich but it's nice if your baseline, risk-free rate of return on cash is 1% or more. The best high yield savings accounts (or money market accounts) offer higher interest rate and there is absolutely no risk. CIT Bank currently leads the pack with the highest interest rate.
Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.