There's a temptation in the messages posted above to say that you only need to worry about the $160,000 limit when performing the discrimination testing, but that's not quite true. Ignoring the limit entirely can lead to crediting too many contributions, most commonly a problem with too much match.
The most common example is a plan that matches 50% of the first 6% of pay deferred. A participant earns over $160,000, elects to contribute 6% or less of his or her total pay, makes $10,000 of elective deferrals, and is credited with a $5,000 match. If one looks at the situation at the end of the plan year, this participant received a 3.125% of pay match (5000/160,000) whereas all nonhighly compensated employees couldn't have received more than a 3% of pay match (50% times 6%). This results in a discriminatory benefit, right, or feature that violates Treas. Reg. 1.401(a)(4)-4. In this particular example, the employer should have limited the match to a maximum of $4,800 per plan year which would have indirectly enforced the $160,000 limit.