Difficult situation.
I used to be a leader at my church's singles group (" College & Career" folks - 20 to 30's) I have also been a high school youth group counselor in church, and was also a team leader on several teen-based missions trips to Africa and Europe. I went to Christian schools all my life, and I have a minor in Biblical Studies from a Christian school (Messiah College - GO FALCONS!

)
Now that I have my 'creditials' out of the way (cough cough), here's my $0.42:
djmcmath: you are absolutely right - there is a large amount of hypocricy amongst single Christian woman. As a matter of fact, there is just about as much hypocricy amongst these woman as there is amongst Christian MEN. (Surprise, surprise!) I have seen and heard way too many Christian men stated "I think it's God's will for us to date," when they
really mean, "I just really want to get into your pants." I also notice that often the guys who 'complain' about how women dress & behave make sure they point out the 'offensive' women to their buddies: "Hey, check out what Melissa's wearing. We need to
pray for her." You might as well say, "Hey, check out the rack on Melissa. Nice!" Hypocrisy is evident on both sides. Note: I am not saying that you do either of the two examples I gave, dj, but that is what I've observed.
Let's be honest - God created woman in a way that is physically attractive for man. This is good. Woman know this, and often make sure that man takes notice of her! Again, to a certain point, this is good - think of it like a coordinated frame to match a pretty picture. It's human nature to like attention. The problem, IMHO, is when instead of
complementing her natural beauty, a woman puts out a NEON SIGN.
There is a time and place for everything. My wife is very beautiful. (Why, she's the most beautiful woman in the world, in my not-so-humble opionion). She wears attractive, but not immodest clothes when we are in public. When we are at home and alone, it's different. Is it wrong for her to run around the house scantily clad? Of course not! (Be glad I didn't say
I run around the house scantily clad - just imagine a visual of me, if you will....

) Some women know how to dress in certain situations, while others really don't understand their effects on men. However, men do have the option to turn their neck instead of gawking at such women.
I know you aren't looking for a solution, but here's a thought - try to talk with one of the girlfriend/boyfriend couples you mention (both the girl and the guy) about the situation - perhaps the girlfriend can give her friends some pointers about what they are wearing and how it effects the male libido.
Something that I would recommend you doing when talking with a woman who may be dressed inappropriately is to talk to HER, and not her boobs. That way, she will know you put more value in HER than her body. BTW: IMHO, the same thing can be applied outside the Christian realm - if you speak to a woman without gawking her, most of the time she will appreciate that more than if you're unclothing her in your mind's eye.
-Z-man.