I took the old sliding doors off in both DD's room and our room. Ours was the first actually. In there, I have a shower curtain on a rod. Unfortunately, you can see the shower curtain rod and the curtains not quite long enough, but I just put new hooks on it - the chrome ones with the rollers - and it looks nice. The curtain doesn't really look like a shower curtain anyway.
In DD's room, so far I haven't put up anything. I have some fabric to match the curtains on her window though. (Sky with clouds and little sparkles.) I haven't got around to sewing it yet. I was waiting until she got a bit older and wasn't hanging on stuff so much, so I probably ought to get sewing now.
I will use a plain curtain rod for her room though. I'm sure she'll like it - she likes to hide in my closet sometimes.
I also have curtains in my kitchen covering the W/D area. I used to have bifold doors but when the old washer died, we got a new set that stacks and has the buttons/dials on the front. The doors wouldn't close. Oops. They were ugly anyway so we took them off. I finally just now put up a curtain rod and hung some cute tab-top panels up there (I got them for $2.49 each on clearance at Linens N Things.)
Our pantry had a bifold door which finally just broke apart. I considered putting up a curtain here as well, but I am still in the market for a new door. I want to be able to keep DD and the dog out of the pantry. Not that it's a huge problem, but I think I'd just prefer a door there. But a solid one instead of the slatted kind - those collect too much dust at my house.