Recently I read an article (http://phys.org/news/2012-11-diverse-post-divorce-parenting.html) which stated that post-divorce parenting arrangements are much more 50/50 than previously thought. The previous arrangement of fathers having every other weekend and one dinner during the week seems to be falling by the wayside. Although this article came from a study in Australia, the same is holding true right here in Pennsylvania, in the 5 county Philadelphia area. It is more likely to happen successfully when the parents live close together, in the same school district, have similar work schedules and the children are older.
Some of the arguments in favor of 50/50 custody are that each parent has the opportunity to be a "full" parent - i.e. helping with homework, putting the child to bed, preparing meals; that the other parent is not relegated to "Disney" parent (all the fun and none of the hard work); that expenses are more equalized. Some arguments against 50/50 are that a parent is only using it as an excuse not to pay child support; that a parent doesn't really want 50/50 custody but wants to "look good"; that 50/50 is not the best arrangement for certain children.
Don't make assumptions about your custody matter. Contact a knowledgeable family law attorney to help you through it.