If you think about the word focus, it is defined as a central point, which creates the dilemma of looking somebody in the eyes. If the eyes were located at the mid-line, it wouldn't be a problem. I think this is part of the reason why we are naturally drawn to cleavage--it's in the middle. It forms one line for the eyes to focus on. It's nature's way of simplifying the task of focusing. Of course this is often highly inappropriate, so you try extra hard to look into the eyes, and avoid the cleavage, taking you further away from the actual topic of conversation. Even without the temptation of cleavage, the eyes present enough of a problem on their own.
I don't know if anybody else has this problem, but I expect there will be at least a couple of people that develop this problem after reading this...
Good luck.
Cheers.