First, the experimental facts:
1. The existence of dark matter was first proposed in 1933 by the Swiss astronomer Fritz Zwicky in order to explain some peculiar kinematic properties of galaxies. Astronomical and astrophysical measurements ever since have confirmed Zwicky's hypothesis.
See: http://en.wikipedia.org/wiki/Dark_matter for details.
2. The fact that the universe is expanding has been known since 1929 when the astronomer Edwin Hubble discovered that the red-shift, or receding velocity of far away galaxies, was proportional to their distance from us. See: http://en.wikipedia.org/wiki/Edwin_Hubble
3. The new wrinkle is the recent measurements in 1998 and later, seem to indicate that not only is the universe expanding, it is expanding at an ever increasing rate.
Those are the facts. Now comes the tough part. How do you make theories to explain all of these facts. Fact #1 can be plausibly explained by postulating a fundamental particle, as yet undetected , that contributes to the total mass of the universe but only interacts weakly with ordinary matter; only through gravity. No problem.
There is nothing strange about fact #2 within the framework of general relativity.
Scientists are still digesting the consequences of fact #3. Theories are a dime a dozen. There are vigorous arguments going on within the physics and astronomy communities about this. One of these theories postulates the existence of "Dark Energy", a mythical property of a "Scalar Field". Other theories simply add an additional term to the Einstein equations of general relativity, a so-called cosmological constant. (This was actually considered and rejected by Einstein)
So the answer is; we don't know.
Now to answer your questions:
Black holes are well understood within the framework of general relativity. They are known to exist, we have a big fat one in the center of the Milky Way. They eat ordinary mater for breakfast and would be happy to swallow any dark matter that comes their way for lunch.
As for correlations between dark matter and dark energy... who knows? Could be. As I said before, theories are a dime a dozen. Experimental facts are harder to come by.
(published on 07/19/09)