I'd avoid putting them in anything where the tone is fairly serious. I see parentheses as being kind of like the author leaning up to the reader and saying something with a wink-wink nudge-nudge, so they're great if you want to mention so-and-so's disastrous first (and last) date with whosit, but not so great if you want to describe the fire-breathing dragon (with really big teeth) that the hero has to face in a dramatic final battle.