  Single crystal neutron diffraction, inelastic neutron scattering and electron
spin resonance experiments are used to study the magnetic structure and spin
waves in Pb$_2$VO(PO$_4$)$_2$, a prototypical layered $S=1/2$ ferromagnet with
frustrating next nearest neighbor antiferromagnetic interactions. The observed
excitation spectrum is found to be inconsistent with a simple square lattice
model previously proposed for this material. At least four distinct exchange
coupling constants are required to reproduce the measured spin wave dispersion.
The degree of magnetic frustration is correspondingly revised and found to be
substantially smaller than in all previous estimates.
