My wife has very small hands, so buying a 1 carat diamond would have made no sense at all. I think I ended up with something around 0.25 carat but went up on clarity. The diamond looked just right on her.
Also, on cost of ring compared to salary, I think I went a little over a month's salary. My wife really couldn't have cared less how much I spent, though. Then again, I don't think I know of a woman who cares less about material possessions.