Baez was asking about what is Lambda in Planck terms just a while ago, here is a PF thread related to that
http://physicsforums.com/showthread.php?t=50108
In this thread our natural units are variants of Planck units (for better or worse) so it doesnt come out exactly the same as in conventional Planck.
Lambda comes out to be 8.46 x 10 ^{121} in natural units of curvatureand as rough idea of the size, that is pretty close to 10 ^{120} which is what quite a few people seem to have been saying
all along.
(E120 is in the same ballpark as 0.846 E120, so good enough for some purposes, and easier to remember)

In that "Planck Lambda" thread I just checked that in these units the cosmological constant and the dark energy density have the same numerical value, which is convenient. You only have to remember one number. And the number is essentially just E120 which is comparatively easy to remember. I tried visualizing the dark energy density as E10 calorie in a pacesize box.
It is also one tenth calorie in a halfmile cube.
figure it this way my fat old Webster's says a traditional regulation "pace" is 30 inches (a "Roman" pace is two steps, twice that, but this is our kind) so "pacing off" some distance is counting steps and 1000 paces is HALF A MILE. Now in these natural units a pace of 81 centimeters or 32 inches is E34.
a half mile is E37
so the halfmile cube volume is E37 x E37 x E37 = E111
and the dark energy density, being E120, can be written
E9/E111
so in a halfmile cube the amount of dark energy is E9, one billionth of a natural unit of energy.
We already played around with this natural unit of energy and discovered that it is 100 million calories (roughly, close enough anyway) and a calorie is E8 of the natural unit.
so E9 is one tenth of a calorie, which is the amount of darkness in this halfmile cube
Well, since we all eat calories (actually we measure food in food Calories which are kilocalories, but yeah we sort of know calories) we have a direct handle on the "observed" dark energy density.
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I dont believe dark energy exists. It could, maybe it will be proven, but I am skeptical and I cant accept it based on evidence to date. What I have more confidence about is Lambda, the cosmological constant, which is a CURVATURE.
that curvature might or might not be produced by some uniformly distributed form of energy called dark energy. maybe it is not the effect of any stuff, maybe it is just an intrinsic curvature that the world has, for some other reason. I am skeptical about postulating an impalpable energy to attribute the curvature to.
curvature is the reciprocal of area.
let's look at Lambda directly. What is the area that is the reciprocal of E120 natural units of curvature?