  Black holes depend only on mass and spin, while what we see from the
accretion flow in steady state depends also on mass accretion rate and (weakly)
inclination. Hence we should be able to scale the accretion flow properties
from the stellar to the supermassive black holes. But the data show significant
differences between these two types of systems, suggesting that we are missing
some crucial physics in AGN. One of these differences is the soft X-ray excess
which is seen ubiquitously in bright AGN, but only occasionally in BHB. Another
is the much faster variability seen in the high energy tail of high mass
accretion rate AGN compared to that seen in the tail of BHB. We show that while
this variability is not understood, it can be used via the new spectral-timing
techniques to constrain the nature of the soft X-ray excess. The coherence,
lag-frequency and lag-energy results strongly support this being an additional
low temperature Comptonisation component rather than extreme relativistically
smeared reflection in the 'simple' Narrow Line Seyfert 1 PG1244+026.
