In article , (Steve
Willner) writes:

In article ,
Bruce Scott writes:
Do we have solid evidence that it is _different from zero_

If by "it" you mean dark energy, yes. There are three independent
lines of evidence: the CMB fluctuations, the SN distances, and baryon
acoustic oscillations. All three agree on the values within their
respective uncertainties.

In the lambda-Omega diagram, each indicates a region where the
combination of lambda and Omega are compatible with the data. Each
region is approximately an elongated ellipse. So, each individual test
allows a range of values (though much smaller than the total parameter
space, i.e. that which was not ruled out before). Since these ellipses
have different orientations, they cross. The interesting thing is that
the intersection of any two also intersects with the third. This
indicates that if the data are wrong, a) several things have to be wrong
which b) just happen to conspire to make it look like a small region of
the parameter space is likely, one which is compatible with other tests
(age of the universe, gravitational lensing, etc). (One can get a
similar ellipse from gravitational-lensing statistics, but those for the
other tests have become so small recently that gravitational lensing is
not competitive at the moment, so while this doesn't appreciably narrow
down the parameters, it does provide an independent consistency check).

and if so what does the curvature of the universe have to be?

The universe is flat to within 0.5% or so.

Meaning |lambda + Omega - 1| 0.5% or so.

I guess [dark energy] is the same thing as "cosmological constant".

The term "dark energy" means something like a cosmological constant
but allows for a more general case where the (negative) pressure
varies with time. So far there is no evidence it does.

Right. That doesn't mean that one shouldn't look for it, but as
observations get better and better and the cosmological constant still
fits the data best, then our confidence in it increases.