  Gravitational waves emitted during intermediate-mass-ratio inspirals (IMRIs)
of intermediate-mass black holes (IMBHs) into supermassive black holes could
represent a very interesting source for LISA. Similarly, IMRIs of stellar-mass
compact objects into IMBHs could be detectable by Advanced LIGO. At present,
however, it is not clear what waveforms could be used for IMRI detection, since
the post-Newtonian approximation breaks down as an IMRI approaches the
innermost stable circular orbit, and perturbative solutions are only known to
the lowest order in the mass ratio. We discuss the expected mismatches between
approximate and true waveforms, and the choice of the best available waveform
as a function of the mass ratio and the total mass of the system. We also
comment on the significance of the spin of the smaller body and the need for
its inclusion in the waveforms.
