The 2007 America COMPETES Act requires that all NSF grant proposals that include support for postdocs must contain a description of mentoring activities. This requirement became effective for proposals submitted on or after January 5, 2009, with a revised procedure implemented for proposals submitted on or after April 6, 2009. Postdoctoral Researcher Mentoring Plans (called mentoring plans hereafter) must be an explicit part of the proposal and will be reviewed under NSF's broader impacts merit review criteria.
NSF's newly revised Proposal and Award Policies and Procedures Guide (NSF 09-29 April 2009), which will be effective for proposals submitted on or after April 6, 2009, includes guidance on the Postdoctoral Researcher Mentoring Plan in the Grant Proposal Guide, Chapter II. Section C2(j): Special Information and Supplementary Documentation. In brief, the mentoring plan is a supplementary document, not to exceed one page, that describes mentoring activities for all postdocs supported by the project.
The April 2009 Grant Proposal Guide, Chapter II Section C2(j), text is quoted here:
Postdoctoral Researcher Mentoring Plan. Each proposal  that requests funding to support postdoctoral researchers must include, as a supplementary document, a description of the mentoring activities that will be provided for such individuals. In no more than one page, the mentoring plan must describe the mentoring that will be provided to all postdoctoral researchers supported by the project, irrespective of whether they reside at the submitting organization, any subawardee organization, or at any organization participating in a simultaneously submitted collaborative project. Proposers are advised that the mentoring plan may not be used to circumvent the 15-page project description limitation. See GPG Chapter II.D.4 for additional information on collaborative proposals
Examples of mentoring activities include, but are not limited to: career counseling; training in preparation of grant proposals, publications and presentations; guidance on ways to improve teaching and mentoring skills; guidance on how to effectively collaborate with researchers from diverse backgrounds and disciplinary areas; and training in responsible professional practices. The proposed mentoring activities will be evaluated as part of the merit review process under the Foundation's broader impacts merit review criterion. Proposals that include funding to support postdoctoral researchers, and, do not include the requisite mentoring plan will be returned without review (see GPG Chapter IV.B.)
 For purposes of meeting the mentoring requirement, simultaneously submitted collaborative proposals, and, collaborative proposals that include subawards, constitute a single unified project. Therefore, only one mentoring plan may be submitted for the entire project.
IMPORTANT NOTE: Proposals submitted between January 5 and April 6, 2009 must follow the slightly different instructions in the January 2009 Grant Proposal Guide, Chapter II. Section 2d(i): Content which specify that the mentoring plan must be included in the 15-page Project Description as a separate section. This is in contrast to the new April 2009 guidelines, which require the mentoring plan be a separate one-page document, supplemental to the 15-page Project Description.
For clarification on the proposal guidelines, PIs are encouraged to contact their NSF program officer.