I was in a relationship where this was a problem...a problem in that it bothered me. I think it was more due to the way he did it. I remember that in the beginning stages of the relationship when we were doing things together, he'd look at women and comment to me about them. One woman he really was going on about how gorgeous she was. Meanwhile, I was too twitterpated to even realize that there were other men besides him on Earth lol. Jokes aside, I think I felt as Lynx described better in post #18. I felt what I had was enough and didn't even have a slight pull to have a look elsewhere.
In this particular relationship, I was left having the same feelings seoulsearch and Lynx describe. As time went on, I realized that this just wasn't the sort of relationship I wanted to be in. I'd rather be content and alone while I "ogle" birds and wildlife lol.
I would also like to add that not only can this be disrespectful to the one you're with, but also to the one you're looking at. I'd be uncomfortable if someone (especially if they were in a relationship) was obviously ogling me and making comments about how hot I am or whistling or singing. I think maturity is attractive. Making others uncomfortable is not.