The delay performance of slow light optical pulses inside photonic crystal slab waveguides is considered in the linear and nonlinear propagation regime from both a theoretical and an application point of view. The numerical model used relies on a nonlinear envelope propagation equation that includes the effects of second- and third-order dispersion, optical losses, and self-phase modulation. It is numerically shown that for rates of $40\mathrm{Gb}/\mathrm{s}$ and $100\mathrm{Gb}/\mathrm{s}$, nonlinear solitary pulses experience less broadening than the linear case and can therefore be used to obtain larger delays. The influence of propagation losses on the soliton broadening factor is also incorporated and discussed. The results demonstrate the potential of implementing a variety of linear and nonlinear signal processing applications in photonic crystal waveguides including optical buffering.