I'd have to say that I do not think that it is appropriate to have comments like this passed between one another, regardless of whether it's man-man or man-women, straight, gay, married or single.
I will tell you that I have long-term friends and we will pass comments between us like "I wish I had your height", or "you have the best calves"; this is all done in a way that is really just bonding and complimenting one another and it's between longtime friends having weathered many of life's trials and tribulations, but genitalia isn't included in those conversations - NOT because it's genitalia but because we all know that size doesn't matter or isn't indicative of someone's manhood. And, to echo other comments you don't know if it's a sensitive or awkward subject for that person (even in the form of a compliment). Likewise I would never comment on a women's body if I don't know her, and if I know her well the comment would be nothing other than how beautiful she is, because in the end I think all naked bodies are beautiful regardless of size, shape, age, etc...
Kevin
Interesting discussion. As to not objectify people, I like to complement choices and values people have that reflect who they are. I like the way you do your hair | how you carry yourself | that you exude a gentle determination. We're all a collection of body parts, some with more say than others. For example, as a man I can become a parent without any impact on my body, but for a woman it's not such a simple equation.