In very high-profile roles, it definitely makes a diff. if you are married or not. This is also dependent on your coworkers and their status as well.
A company will always play the "dedication" card when it comes to work. IE, if you are married and have young kids, they can say you know what, John is too busy, he can't put in the time required for project whatever.
This is obviously not right but when have companies actually listened to and practiced corporate responsibility? Stating that they are 'equal opportunity' is simply a formality in their eyes. When it comes down to it, they want someone that can put in 300 hours per week (if need be) to finish a project. When it comes to someone that has a family and has obligations to that family (pick up the kids from school, take care of them, etc etc etc), they will most likely lean towards someone that does not have these "restrictions" - someone single - someone who can come to the office for 300 hours this week to finish project whatever.
FWIW,
- tsd