Mouse polling rate
If you have invested in a high resolution mouse, adjusting the USB polling rate is a common trick to utilise the added precision it brings. The polling rate (or report rate) determines how often (per second) the mouse sends information to your computer. Measured in Hz, this setting equates to lag time (in ms).
By default, the USB polling rate is set at 125hz. The table below represents combinations of Hz values and their corresponding delay time:
If the polling rate is set at 125 Hz, the mouse cursor can only be updated every 8 milliseconds. In situations where lag is critical (for example games), it is useful to decrease this value to as little as possible. Increasing the polling interval will improve precision at the tradeoff of using more CPU resources, therefore care should be taken when adjusting this value.
CS:S Mouse Optimization Guide -- largely aimed at Windows users, though the same principles apply for Linux.