I suppose it depends on what it is, and also whether a spouse is themselves in the mood for being vented to (and possibly upon!
). Also, there are just some things that might be better served in another friendship or relationship.
My dh is as supportive as the day is long. But when it comes to my academic work, even though I know he *feels* supportive (and is; I couldn't do it without him), if I want someone to say the "right" thing, well, I finally realized the right thing would sound weird coming from dh; it wouldn't be him, it wouldn't be natural, it might even be creepy!
A friend of mine already done with med school says the right things. So I email him when the academic pressure is building, he says the absolute right things that no one else seems able to, I feel fabulous, and I even feel more receptive to dh's and other friends'/family members' words of support, which would have made me cranky otherwise. It's silly semantics, and I am grateful for everyone's kind words and feelings and I know they're all rooting for me. But even in other situations there are some conversations that are just more fun (especially complaining!) with different friends.