  We discuss in the framework of the excursion set formalism a recent discovery
from N-body simulations that the clustering of haloes of given mass depends on
their formation history. We review why the standard implementation of this
formalism is unable to explain such dependencies, and we show that this can, in
principle, be rectified by implementing in full an ellipsoidal collapse model
where collapse depends not only on the overdensity but also on the shape of the
initial density field. We also present an alternative remedy for this
deficiency, namely the inclusion of collapse barriers for pancakes and
filaments, together with the assumption that formation history depends on when
these barriers are crossed. We implement both these extensions in a generalised
excursion set method, and run large Monte Carlo realisations to quantify the
effects. Our results suggest that effects as large as those found in
simulations can only arise in the excursion set formalism if the formation
history of a halo does indeed depend on the size of its progenitor filaments
and pancakes. We also present conditional distributions of progenitor pancakes
and filaments for low-mass haloes identified at present epoch, and discuss a
recent claim by Mo et.al. that most low-mass haloes were embedded in massive
pancakes at $z\sim 2$.
