Coming from someone who had them/has them fading, its safe to say it is not worth it. Why do you need them? To impress girls? Sure, I got compliments for them by women, but nothing ever came from it. Flat and solid, like NeutralDrow said, is probably for the best. You don't really want a truly defined six-pack either. I found that one that is almost...shall we say, hidden, is the best one to have. For example, if you stretch/lean a certain way and they come out, that is the "six-pack" I'm talking about =P
I do have to agree though, there is nothing wrong with working out/staying fit and healthy! I still do sit-ups from time to time, but nothing to keep my six-pack around.
I'd also like to add that, just like anything else...you're going to have to stick with it. The moment you let that one day of exercise pass you by, it all goes downhill.