Ruth, at best, put herself in a sexually compromised situation with Boaz where Boaz told her not to tell anyone about it. At worst, given the connotations of the Hebrew words, she exposed his genetalia and approached him seductively (Ruth 3:1-14); and she was heralded as a righteous woman (3:11)
This one fascinates me. I just read it again in devotions. Yes, the feet was sometimes a euphemism for private parts, but I'm not convinced here. I only found the eupehmistic use towards the bottom of my Hebrew dictionary, anyway. The word "lie down" is also interesting. It can mean sexual relations, or an act of submitting oneself to another. Which is it? I think the context of Ruth putting herself before Boaz, but waiting for him to act tells us there was no hanky-panky going on. It may also give some balance to how guy-girl relations should work these days! (Nothing wrong with perfume and nice clothes, but wait for him, don't lead him along or manipulate him.) I think the reason Ruth does this is the same reason Tamar goes after Judah. This was the only means she had to seek out her redeemer-kinsman. Given the culture, to approach him in daylight one on one would have cast her as a shameless harlot. Funny, but all the women in that Matthew 1 geneology (Rahab and Bathsheba are the other two) have this in common: they find themselves in hard situations, and commit acts of bold faith (some of which are or appear to be morally questionable) to resolve the situation.
As to the Ruth instance, I don't think our notions of morality would permit any unmarried woman to make herself desirable and lay down next to another man. The comments I have found on this passage all point out the ambiguity of the words used describing what happened that night. "uncover" "feet" and "lie down" all have sexual overtones and yet the narration does not explicitly say something sexual transpired. In addition, threshing floors were a place where only men slept and so a woman at the threshing floor would make Ruth to be a prostitute, and the threshing floor setting in ancient Israel suggested sexual compromise (Hosea 9:1), with the parallels of "treading" and "fertility." The whole setting and buildup compare to modern soapoperas where the suspense is around whether they "did it" or not.
Our notions of morality are not always the best definition of righteousness. Jesus blasts the Pharisees for doing this (Mark 7:6-13). Sometimes loving our neighbor calls for violating our /notions/ of morality.
The terms have sexual /possibilities/ but not those overtones every time it is used. The same verb "lie down" appears in Gen 28:11, where Jacob goes to sleep, fleeing Esau, and dreams the ladder. There is no sexual overtone there, given the context. Ruth's context is different, but I believe any overtone of sex is meant to show that Ruth's goal is to marry Boaz - future sex, not present. I've seen similar readings of Ruth as soap opera - had it in seminary, in fact - and reject it as eisegesis: reading our modern sensationalism into the text. The sexual overtones simply reflect the nature of Ruth's request. Both Boaz and Ruth's faithful righteousness are pointed out in other places.
Interesting threshing floor picture. I love that kind of thing. I'd say it could also be a positive image of bread being produced in Bethlehem: the Bread of the world, that is. Bethlehem meaning "house of bread," after all. Threshing and treading were also joyous harvest times. But I get your point that a woman at the threshing floor at night is unorthodox and gives the appearance of impropriety. But again, to automatically equate the appearance of sin with immorality is a gross injustice when they are not in fact the same. Personally, I think in heaven there will be a LOT of apologies to Ruth from today's scholars for making such suggestions.