I have had some married couples as officers in my guild. There were a lot more than there are now.
I usually found that when one had a strong opinion about something, the other would stay out of it, which is probably the best way to go, really.
In a situation where both are voicing the exact same opinion, it's difficult to determine if both agree independently from each other or simply agreeing with their significant other because (s)he is their significant other. My tendency would be to count their opinion as a single one, rather than two.
If people are just counting their opinions without taking that into consideration, then that could definitely throw things out of whack.