I kinda am wondering that myself. I don't see why they wouldn't. Weight is a form of resistance. So if weights work, resistance bands should work too, right? Let's see if anyone else knows.
I just picked up my first resistance tube. I have lifted weights pretty intensely when I was in college, so I was pretty skeptical about the little bands. I bought a red xertube from Spri. It is the medium resistance. It comes with a door attachment so you can use it on the back of a door for more variety of exercises.
I was pretty impressed with it. It is WAY better than that Thera band stuff they give you in Physical Therapy. It has comfortable handles and you can definately feel the resistance.
Just make sure that you get decent quality ones, I have seen some pretty poor quality ones and they don't last. The Spri ones seemed very nice.
The feel of the resistance bands was awkward for me. That might have just been due to the fact that they weren't the best quality, but the resistance of weights and gravity seems more comfortable in my opinion.
The cords I have used in past did offer some resistance and were ok for certain movements. I have bands, but I only like them in conjuntcion with pilates/yoga movements b/c they feel awkward. After a short period of time your muscles adapt to them and you need different movements as well as different weights (big and small mucsles require light and heavy/heavier weights) which bands and cords cannot/do not offer.