I don't know, maybe this isn't as big a deal as it seems to me. But I was always skeptical of the idea of dark matter, as it seemed like a cop-out. Scientists had no way to account for all the mass that their equations must be there, so they decide that it's a form of mass that they can't see.
Now that there's some proof of its existence, it changes things. I've got to pay more attention to the news though. The first I heard of it was from reading a webcomic.
This has always made sense to me, as it explains to me (I think, I'm not an expert) how light could have zero mass but be affected by gravity. If light is simply a wave and not a particle and a wave, then it makes much more sense. Light could simply be the movement of a wave of visible energy through dark matter, and the dark matter could be affected by gravity.
Also, it seems cool to me that the universe could be expanding out due to an actual vaccuum beyond the dark matter, which is getting stretched out like a giant puffing marshmallow.
Wow, from $100 to the mailman to not tipping the waiter. Here's why I don't tip the mailman (actually, to be honest I never tip the mailman because it never really occured to me. But here's my rationalization).