  Recent theoretical work has shown that so-called pulled fronts propagating
into an unstable state always converge very slowly to their asymptotic speed
and shape. In the the light of these predictions, we reanalyze earlier
experiments by Fineberg and Steinberg on front propagation in a
Rayleigh-B\'enard cell. In contrast to the original interpretation, we argue
that in the experiments the observed front velocities were some 15% below the
asymptotic front speed and that this is in rough agreement with the predicted
slow relaxation of the front speed for the time scales probed in the
experiments. We also discuss the possible origin of the unusually large
variation of the wavelength of the pattern generated by the front as a function
of the dimensionless control parameter.
