Who reads the NSF postdoc fellowship applications? (mathematics)
Some NSF programs are reviewed across sub-disciplines with reviewers that present a cross-section of mathematics. If memory serves me right, then that's true for CAREER proposals, for example, and I think also for the postdoc fellowships. In those cases, you'll have to expect that your audience consists of people in applied and pure mathematics, and you will have to find a level that keeps both of these groups interested in your proposal.