I think it depends in part on how well you can set your boundaries. My wife and I worked together for several years before I went into real estate. After awhile, work became almost all-encompassing: no matter where we were, I was still hanging out with a co-worker, and half of our after-hours discussions wound up being about work. Not to mention, after spending hours commuting together, then being in the same suite of offices all day, then commuting home together, quite often we just wanted to NOT be around each other once we got home.
Yes, it was great working with someone who I could count on to be honest and trustworthy...but it did also place other strains on our relationship to which we had to adjust.
Now, a far as real estate is concerned...My highly unscientific observations have suggested that husband/wife teams tend to be more successful than teams of unrelated agents. With both partners in the field, each can appreciate their partner's unpredictable and hectic schedule (this also seems to be true in the scientific field, where I worked beforehand). And often, the balance between each person's strengths and weaknesses that makes them a successful couple also makes them successful partners in business.