When you're in the defined contribution retirement plan, your employer makes a base contribution of 5% of your salary, not including bonuses, commissions, overtime, room and board and utilities.
If you also contribute, your employer may match your contributions. (Most employers match up to 4% of your salary.)
2010 contributions
In 2010, you may contribute up to $16,500 before taxes if you are under age 50, and an additional $5,500 if you are 50 or older. The combined total that you and your employer contribute may not exceed 100% of your salary or $49,000, whichever is less.
Employee contributions are deducted from your paycheck on a pre-tax basis. You may change the deduction as often as you want, or you may stop contributing altogether, if you choose.