I've never understood this "emotional affair" thing. If a man is emotionally close to a woman who is not his wife, but they never cross the physical line, how is that cheating??? I think women just made that up because they feel that they should be the only woman their man confides in or shares with emotionally.
The real issue is that if you actually fall in love with another woman, it becomes much more likely that you WILL cross the line physically.
As for SC extras, I think that's just flat out cheating. Hell, a lap dance without extras is probably cheating.
But at the end of the day, I agree with sharkhunter: the two people in the marriage need to decide for themselves what is and isn't out of bounds for their relationship - regardless of what other couples might decide. Then if you go outside of those boundaries, you know you're cheating.