There have been reports in the media - and a discussion at Cosmic Variance - that according to some observations of B.S. from Louisiana, the cosmological constant is not constant after all. Instead, it seems to be changing with time. It has been argued that this is implied by the observations at the 97% confidence level.
The corresponding equation of state would give "w" (the pressure/energy_density ratio) smaller than "-1" (much like in models of phantom energy) which would violate the dominant energy condition - and potentially allow superluminal signals. This sounds highly suspicious. Gamma ray bursts had to be used for the analysis - and they are sufficiently poorly understood - and independent experimental astrophysical sources at Harvard also recommend you to ignore the news.