The NY Times had an interesting piece recently by J Conlin called "Living Apart for the Paycheck"
The Census Bureau reported in 2006 that 3.6 million married Americans (not including separated couples) were living apart from their spouses. It quotes Prof. David Popenoe, who I've known for many years; he's brilliant. There are certainly challenges in one of these marriages, but I have to say that I believe it is possible for a strong marriage to endure this, but not for a sustained period of time. One of the best points Conlin makes is how the bulk of the responsibilty for the children falls on the at-home mother. She has to be the disciplinarian while her husband comes home from afar and gets to be "Mr. Fun". Nice plug for Skype too (Online Maven take note!). It's a quick and worthwhile read; I recommend it.