Review your 401k account and its balances. Within your 401k plan, some investments will have done well, while others may have done poorly. This does not mean that it is time to sell the lower performing ones in order to buy the higher performing ones. This is called chasing performance, and it is one of the worst kinds of market timing to engage in.
Instead, evaluate your investment options only against the other investment options of the same type. For example, evaluate your Small Cap investment funds that you were invested in during 2009 against the other available small-cap funds that are in your plan. If there is a considerable disparity, consider allocating some dollars away from the underperfomers, but only to other investments of the same time.
Next, review whether or not the overall allocation still makes sense for your personal situation. If you are nearing retirement, you need to make your 401k more conservative. If you still have ten years to retirement or more, now is not the time to get more conservative. Whether the market and the economy recover in 2010, 2011, or 2012, you have the time to wait for it to happen. Getting conservative now, will only cause you to miss out on the returns you need to recover from the massive retirement losses most people suffered in 2008.