filthy under wear 
I see a lot of people responding without clarifying what metaphysics actually means. So let's be clear:
There is a lot of pseudoscientific bullshit that gets labeled as "metaphysics" -- aura reading, psychics, Deepak Chopra, misunderstandings of quantum theory, and so on. Basically, read "metaphysics" and "pseudoscientific explanations that sort of sound like physics."
The word "metaphysics" has been used a lot longer in philosophy, and it means something entirely different here. Depending how you count, Philosophy has a few major branches -- here's two:
Metaphysics -- what is the nature of reality?
Epistemology -- how do you know that?
In this sense, metaphysics is a perfectly valid line of inquiry, but you wouldn't want to entirely dismiss epistemology. I could come up with a very elaborate picture of how the universe might be, but that's usually not all that useful if I don't have a good reason for thinking this is actually true.
Here's an example of where a metaphysical argument might be more satisfying than an epistemological argument: How do we know we're not in The Matrix? And if we are in something like that, how do we know that any of our beliefs are true? After all, if I've lived my whole life as a brain in a vat hooked up to a simulation, I have no way of knowing if I'm even human, or if anything like a human actually exists anywhere in the real world, right?
Epistemology can't say much about this. We can discard certain types of simulations by arguing about the amount of computational power required, or maybe even showing that certain physical properties of the universe are uncomputable -- but how much can we really say about what's computable by a computer we've never seen before, in a reality we've never seen before, with some laws of physics we've never seen before?
On the other hand, there's a sound metaphysical argument that it doesn't matter. When we discovered that everything was made of atoms, it didn't change what we already knew. We once thought wood was an element, but a wooden table is still a wooden table even if the wood is really made of atoms. Nor did all of our atomic theory suddenly stop being true when we discovered that atoms are made of quarks. If we discover that, at some very fundamental level, everything we know of is made up of bits, it wouldn't make it any less real.
So we still can't know, from an epistemological perspective, whether or not we're in The Matrix. But from a metaphysics perspective, we can know that even if we are in The Matrix, very nearly every belief we hold about reality is still as true as it ever was, except maybe very specific beliefs like "I believe I'm not in The Matrix."
So from a philosophical perspective, metaphysics is still a valid line of inquiry. But even philosophical metaphysics can be a waste of time if it's completely ungrounded. And the colloquial definition of metaphysics is even less grounded in reality. I would generally apply epistemology to that -- how do you know I have an aura? "I just feel it" isn't a good enough answer.
