Management fee waivers are a tax-minimization strategy employed by private equity firms to essentially have management fee taxed at capital gains rates rather than at ordinary income rates. There's a recent article from NY Times DealBook called "What's at Issue in the Private Equity Tax Inquiry" that provides a good overview of management fee waivers and why the New York Attorney General is reportedly investigating the practice.
Here's the link:
http://dealbook.nytimes.com/2012/09/04/whats-at-issue-in-the-private-equity-tax-inquiry/