Good point MacNFries.
There are some pretty important psychological differences between true cuckolding, hotwifing, swinging, and open marriages. There are probably plenty of places where they overlap, but the power structure is different.
And I think there's a spectrum of ways to do this. I see some guys here are into 100% submissive, dom wife, humiliation, chastity devices and no sex for the cuck. And some even who see a sexual cuck aspect to the idea of the bull getting the wife pregnant. That's probably about as extreme as I can imagine short of her castrating you with her bull's hunting knife.
Toward the other end of the spectrum would be what I'm looking for where my wife takes a lover or at least lands a few studs and her increased sexual freedom leads to a richer happier sex life for us together.
I think Mac is probably right that many guys encourage their wives to take lovers so that they can get a girlfriend. I guess at some point, this kind of lifestyle leads to the other extreme that I wouldn't want to see happen in my own marriage, namely falling in love with other people and splitting up. If there was any indication that our sex games were leading to a weaker relationship, I think we would stop immediatly and get our house in order before proceeding.
As for the original question of this post, as to how many guys have feelings to be both cuck sometimes and a bull others...
For me the way I rank things
1) Sex with my wife
2) Sharing my wife with another man in a threeway
3) Watching my wife fuck another man while I watch
4) Watching my wife with another woman while I watch
5) Swinging/partner swapping
6) Dropping my wife off to get fucked me not in the room
7) me in an FFM threeway with my wife as one of the F's
8) Being the Bull and cucking some other guy
9) jacking off
I've only done 4 of the above. Hopefully with a little advice from these forums, I can add to that number!