In the past I have saved submerged, just off Scotland, in the middle of being DC'd and it's been fine, but now I'm getting better in my careers I'm more careful with my saves but still occasionally save within the recommended distance of other vessels. All is ok so far! These closer saves are when the wife is hovering with the rolling pin, taking carefull aim.
In XP (where I wasn't so careful) I guess that somewhere between one in five and one in 10 would be right (that would be one in 7.5 then), but some people still have problems even when they think the save is a good one!