is replacing windows (not the OS kind) worth it?

[thermarest]

I asked this question of the inspector I hired for a pre-purchase for a 1976 house with wood windows. His firm opinion was that in terms of cost savings via energy conservation new windows were not worth it. But there are plenty of other reasons to get new windows--you don't like the drafty feeling, you want them to open and close smoothly, want a certain look, want to see out better (frosted or "smoked" old windows).

Doing it yourself is totally reasonable, depending on your level of DIY determination. If you enjoy that kind of thing and have a friend who has done it before and/or a complicit spouse, I'd say go for it.