  Recent evidence - in particular the hard X-ray spectra obtained by NuSTAR,
and the large amplitude hard X-ray variability observed when ultraluminous
X-ray sources (ULXs) show soft spectra - reveals that common ULX behaviour is
inconsistent with known sub-Eddington accretion modes, as would be expected for
an intermediate-mass black hole (IMBH). Instead, it appears that the majority
of ULXs are powered by super-Eddington accretion onto stellar-mass black holes.
Here, we will review work that delves deeper into ULX spectral-timing
behaviour, demonstrating it remains consistent with the expectations of
super-Eddington accretion. One critical missing piece from this picture is the
direct detection of the massive, radiatively-driven winds expected from ULXs as
atomic emission/absorption line features in ULX spectra; we will show it is
very likely these have already been detected as residuals in the soft X-ray
spectra of ULXs. Finally, we will discuss ULXs that do not appear to conform to
the emerging ULX behaviour patterns. In particular we discuss the implications
of the identification of a good IMBH candidate as a background QSO; and the
confirmation of an IMBH/ULX candidate in the galaxy NGC 2276 via the
radio/X-ray fundamental plane.
