The other day I sighed after finishing a wonderful piece of chocolate cake. My friend asked why I sighed. Rather puzzled, I explained that the piece of cake she had given me was amazingly delicious and that my sigh was happy, satisfied sigh. She replied back that she always thinks of a sigh as having a negative connotation.
I told her that to me a sigh can be negative but it can also be positive meaning contentment after having completed something enjoyable (or even a task that was difficult and one sighs as a pleased sense of accomplishment). She disagreed and said that I was incorrect because a sigh is not usually associated with something positive.
When we looked up the official definition via several dictionaries, she looks to be correct about the word sigh being used with negative connotations (as in expressing relief, exasperation, disgust, etc.).
I'd be curious to hear as to whether anyone else thinks it's acceptable to use the word sigh to express a positive feeling.