Used or New?

At the risk of asking an age-old question... My current car (a 1992 Buick) is getting older as the months go by, and I'm trying to figure out what I want to settle on when it finally is time to say goodbye to it. I like the Prius for its fuel economy and for the reliability I hear that it has. However, I find it hard to justify the cost compared to other vehicles, and more generally it's hard to justify the cost of a new car compared to a used car (I guess I'm a penny-pincher).

So.. if I do settle on a Prius, would you suggest I consider a used one (probably the newer generation of 2004 and up), or should I just suck it up and pay more for a new one? Anyone have advice on things that are conspicuously different about the different model years (beyond what the specs make obvious)?

Thanks for entertaining this very basic question -- if the same thing has been discussed on other threads that I didn't see, feel free to redirect me.