I just did them for my daughter's room a couple of months ago. They are straight but have three tiers of ruffles (about the size of the ones in that picture in the previous post) at the bottom. They came out pretty cute actually. I thought it would be much easier making the ruffles after watching a tutorial, but my sewing machines widest stitch ended up not being wide enough. I ended up doing the gathering and stitching of the ruffles by hand, sewing them to the backing piece of fabric, an then removing the hand sewn thread. I don't know if that makes sense, but it worked nicely. I'll see if I can post a pic later.
I actually did something very similar back in October and I love how they turned out. I made lined curtains (which was super simple), and then hand gathered the ruffles using basting stitches (I did 5 rows of ruffles). It wasn't necessarily hard, but it was time consuming (though nothing you can't do while watching tv or the like). And it does take waaaay more fabric than you would think. I think I spent around 3 days and $80 to make them -- so it depends on how much time = money to you.