The jury is still out on this one for me. I agree with the posts that imply that how we dress reflects what we expect when we come to a worship service. Do we expect to be preached to by a man only, or do we REALLY come expecting to be in the presence of a Holy God?
I HATE to dress up, and rarely do it, even at church. If I'm not wearing jeans and sneakers then I feel very uncomfortable. (I get hot and sweaty very easily) However, I try to wear a nice shirt and clean sneaks or even black or brown shoes to "step it up a notch." But I've got to tell you, the only reason why I don't really dress up for church is simply because I hate it so much! I would love to justify it by saying that God only looks at the heart (and I'm not implying that those who use that argument are simply justifying it. I think they're fully convinced in their own minds and therefore, not sinning.)
But if I have to perform a role, such as teaching or communion, then I dress much nicer.
As for the young ladies immodestly dressed, I think its for the women to correct them. And if the women are not correcting them, then we should go up to those women and say, "Hey, see so and so? It would be great if you could encourage her to dress modestly for the worship service for these reasons..."
I'm at the point now where I'm very tempted to go up to these females and say something to them myself! Seriously. The job is just not getting done and I'm tired of them flaunting their tight buttocks all over the sanctuary like they're there to pick up guys, or at least cause them to drool.

(But I'll say it in a very tactful and winsome manner)