By Lisa Ryan What's the ideal number of sex partners? MSN's survey highlights what men and women say, plus relationship expert Susan Winter. Some people want their significant other to divulge how many sexual partners they've had, while others would rather keep that information under wraps. But those who choose to share may be curious to know how their numbers "line up" with others — and whether the number of sex partners they've had would be considered ideal. And now, a new survey of 2,000 adults in the U.S. [...]