Here is a paper criticizing the often-cited "4% rule".

http://papers.ssrn.com/sol3/papers.cfm?abstract_id 05652 Efficient Retirement Financial Strategies William F. Sharpe, Jason S. Scott, and John G. Watson July 2007

"Unfortunately, the 4% rule represents a fundamental mismatch between a riskless spending rule and a risky investment rule. This mismatch renders the 4% rule inconsistent with expected utility maximization. Either the spending or the investment rule can be a part of an efficient strategy, but together they create either large surpluses or result in a failed spending plan.

,,,

Overall, our findings suggest that it is likely to be more fruitful to clearly specify one's assumptions about a retiree's utility function, then to establish the optimal spending and investment strategy directly. Of course, one should take into account more aspects of the problem than we have addressed in this chapter. Annuities should be considered explicitly, rather than ruled out ex cathedra. Separate utility functions for different personal states (such as "alive" and "dead") could be specified rather than using a weighted average using mortality probabilities, as we have assumed here. Yet our analysis suggests that rules of thumb are likely to be inferior to approaches derived from the first principles of financial economics."

http://papers.ssrn.com/sol3/papers.cfm?abstract_id 05652 Efficient Retirement Financial Strategies William F. Sharpe, Jason S. Scott, and John G. Watson July 2007

"Unfortunately, the 4% rule represents a fundamental mismatch between a riskless spending rule and a risky investment rule. This mismatch renders the 4% rule inconsistent with expected utility maximization. Either the spending or the investment rule can be a part of an efficient strategy, but together they create either large surpluses or result in a failed spending plan.

,,,

Overall, our findings suggest that it is likely to be more fruitful to clearly specify one's assumptions about a retiree's utility function, then to establish the optimal spending and investment strategy directly. Of course, one should take into account more aspects of the problem than we have addressed in this chapter. Annuities should be considered explicitly, rather than ruled out ex cathedra. Separate utility functions for different personal states (such as "alive" and "dead") could be specified rather than using a weighted average using mortality probabilities, as we have assumed here. Yet our analysis suggests that rules of thumb are likely to be inferior to approaches derived from the first principles of financial economics."