I've only been using dry shampoo for about a year now, and have no idea WHY I haven't been using it my entire life!
(Well, yes I do. I simply didn't know about it. Maybe like you?)
This is one of those make-life-easier sanity savers on mornings when you just don't have time (or energy) to wash/style/etc whatever is atop your head. Just lift roots in sections and spray! (Don't spray too much, though, or your brown hair will appear to be graying.)
I run a quick burst along the root, and then sweep it about half-way up the strands for good measure.
Let it sit for a couple of minutes, then run your fingers up your scalp, from bottom to top, and tousle.
Not only will most of the greasy be gone, but it will give your roots a lift and boost volume.
Don't style it too much after you've sprayed, or you'll begin to bring back the limp, greasy strands you were trying to get rid of in the first place.
I also recommend this if your hair is thinning and you struggle to get volume to cover those now-not-so-covered spots. =^)
you can find them for a few dollars at Target in the shampoo aisle.
(I think I'm going to switch back when I'm done with this can.)
And if you're willing to spend a bit more money (which, I'm not), many salons offer dry shampoos that match your hair color, so you don't have to worry about any ashy-looking strands.
Just make sure you get one that smells pleasant. *wink*
The other benefit is your hair thanks you. So many of us are washing it way too often! Especially in dry climates (Hellloooo, Colorado!), this can lead to damaged hair with split ends because (as much as we don't want the grease) our hair needs some of that oil to stay healthy.
Give it a little break and extend your hair-wash cycle by one day!
Look at this funny ad I found from the 70's. So, maybe you've all known and it was just me who's been in the dark? =^)