I've sewn many a set of curtains, but I never thought of knitting window treatments. Now that I have, it actually seems like a sound idea for sheer-type window treatments: they can be knitted in any size, colour, and texture you wish, and it will drape beautifully. The pattern for the picture above is available on KnitPicks.
Here's another knitted curtain pattern from Joanne Seiff on Ravelry. There's no need for a knitted curtain to be white lace. It can be any colour you like, and have a modern and minimalist yet interesting texture.
Here's another window treatment idea from Lion Brand. This one doesn't involve actual knitting, and just requires a novelty yarn, beads, and a lot of knotting and tying.
This, of course, is filet crochet, not knitting, but if you want a sheer with any kind of image in it, filet crochet allows for endless possibilities.
Coming up: Look for a review of the Knit n' Style Summer 2013 issue tomorrow!