Is the expression 冰雪聪明 (bīng xuě cōng míng) really only used for girls? The literal translation is "snow smart" and I understand it means something along the lines of "extremely smart" but the times I've tried using it for boys/men I'm told it's only for girls.
冰雪聪明 always describes that someone is very clever and smart. It comes from 唐·杜甫《送樊二十三侍御赴汉中判官》诗：“坐知七曜历，手画三军势。冰雪净聪明，雷霆走精锐。”. But 冰雪聪明 is not only for girl.
冰雪聪明 can be used to describe the child too----冰雪聪明的孩子, but be careful when you use it to describe adult, especially male adult.
Other examples in ancient articles:
以冰雪聪明的文章，写雷霆精锐的思想，这种议论，就容易动人听闻了。（清·曾朴《孽海花》第十回）
姬冰雪聪明，靡不淹悟，类多韜匿不言。(清·陈孟楷 《湘烟小录·香畹楼忆语》)
Source：
I would say, in most cases it is used to describe young girls. In some other cases, if people want to make their comments/conversation to take a flavor of humor, they can be used to describe boys/men.
才貌双全 is relatively more neutral.
According to baidu (http://baike.baidu.com/view/117274.htm), it is usually used to describe women, but can occasionally be used to describe men as well. "这个词通常用来形容年轻女子。 ... 有时也可用于才貌双全的男性。"
Yes. This word is ususally for girls.
cōng ming. – Stan Jan 6 '14 at 2:04聪明alone can be pronounced ascōng ming, and it is quite often heard; however it's not a must, the National Putonghua Proficiency Test doesn't put it in the "must neutral tone" list, and the 现代汉语词典 fifth edition also marks it ascōng míng(well it is a constant argued issue). In冰雪聪明, thecōng mingsound is not natural, so at least I don't suggest pronouncing it like that. – Stan Jan 6 '14 at 4:23