I'm a stellar astronomer and not a cosmologist, but perhaps that's better for your broad gauge question because I can take a more historical view.
I recall very well papers in the early 70s which exhibited the classic Hubble plot of recessional speed vs. some distance metric. At the time some researchers claimed a putative "q" value for acceleration, or at the least claimed an unambiguous answer was to be found before the decade was out.
Thirty years have now gone by, and while H (the Hubble Constant) has stabilized considerably (wags used to call it "Hubble's Variable Constant") the further refinement of how H varies with distance, which determines in part what value a cosmological constant must have, is still, I believe, quite open.
Although the actual formalism to describe what observations of the Universe imply for cosmology is somewhat different (these days, instead of the "acceleration" parameter q we speak of capital Lambda, the cosmological constant, and capital Omega, the density), in my judgement the data is still not good enough to unambiguously resolve this question. Particle theorists, who jump from theory to theory with the greatest theological promiscuity of any scientist, interject reasons why the universe *must* be a certain way, not on the basis of any observed fact, but on tidbits of elegant mathematics which suggest themselves for a time.
The latest hullaballoo about the cosmological constant stems from measures of distant galaxies inferred from the brightness of a certain type of supernovae observed therein. Until we have different and complementary metrics (some other suggested ones already disagree considerably), we can't have confidence in the measure.
I'm not saying that it's a bad thing that so many ideas are fermented in these times, only this cauldron is viewed as tentative and exploratory by those involved. This distinction is lost in reports to the media, which tend to lose the professional's distinction between ideas that are interesting but half-baked and those which rest on multi-faceted observations and have stood the test of time.
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