i did an informal survey of major publisher's web pages:
random house: all the books featured in the "fiction section" were by females authors. the books featured in the "nonfiction section" were split between male and female authors: one co-authored text by a male and female, one male single author, and one female single author...
I even refreshed the page to see if the titles were randomly generated, they were not.
Penguin: under featured fiction, there were two female authors and four male authors noted. but under the news section, there seems to be a smattering of both genders mentioned.
those are the only two i went through so far. also, a quick peek at the nytimes bestsellers list may also reveal how well gender are selling, but it also depends on how many books are out by big names like king, steele, rice, cussler, grisham, etc. they tend to top the list and stay there for awhile.