Keith, from a recent preprint:

"Marginal evidence for cosmic acceleration from Type Ia supernovae"

by: Jeppe Trøst Nielsen, Alberto Guffanti, Subir Sarkar


Abstract:

"The "standard" model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present --- as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these "standardisable candles" indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion."

http://arxiv.org/abs/1506.01354


I don't know the first two authors, but Sarkar is Professor of theoretical particle physics and cosmology at Oxford University, and extremely eminent.

Dust has long been one of the big caveats with this result.