To me, it all seems wrong.
The source behind the custom of breaking the glass is a Gemara in Brachos 30B-31A (Soncino Translation found here - bold headers by me):
Introductory section: "What is meant by ‘rejoice with trembling’? — R. Adda b. Mattena said in the name of Rab: In the place where there is rejoicing there should also be trembling. Abaye was sitting before Rabbah, who observed that he seemed very merry. He said: It is written, And rejoice with trembling? — He replied: I am putting on tefillin. R. Jeremiah was sitting before R. Zera who saw that he seemed very merry. He said to him: It is written, In all sorrow there is profit? — He replied: I am wearing tefillin.
The part relevant to this post: Mar the son of Rabina made a marriage feast for his son. He saw that the Rabbis were growing very merry, so he brought a precious cup worth four hundred zuz and broke it before them, and they became serious. R. Ashi made a marriage feast for his son. He saw that the Rabbis were growing very merry, so he brought a cup of white crystal and broke it before them and they became serious."
So you see why I'm conflicted about this. The breaking of the glass is meant to be an appropriate spiritual imposition/reminder at the very height of the joy experienced by the chosson (the moment of marriage under the chupah) - and a sign to everyone else - that despite our great happiness, life isn't what it could be, since we don't have the Beis Hamikdash.
An additional point regarding the meaningfulness of what Rav Ashi (and seemingly Mar brei d'Ravina) did in smashing the white crystal (according to a Tosafos somewhere in Shabbos that I can't find) was that the white crystal was a plentiful resource during the time period when the Beis HaMikdash stood. After the destruction, it was no longer found and became a scarce commodity. Hence, smashing the white crystal goblet was like destroying a relic from the Beis HaMikdash itself, compounding the significance of performing such an attention-grabbing action.
One solution, which Rabbi Elyashiv Knohl presents in his book Ish V'Isha is to break the glass during the singing of Im Eshkocheich. The placement of the glass breaking during the song that reminds us (and the chosson specifically) to not be too joyous by remembering that we are still in galus and without the Beis Hamikdash, thereby reminds us just why we do it in the first place. Rabbi Knohl also remarks that by doing this the singer will hopefully drown out the one awkward guy who shouts "Mazal Tov" anyway when the glass is smashed.
I was discussing this topic with a married friend of mine recently, and I asked him what he did (I couldn't remember). To my surprise, he said he broke the glass at the end in the typical fashion seen at most weddings. He is certainly the personality/hashkafic type who I had presumed would break the glass during Im Eshkocheich, so I eagerly asked him to explain why he didn't do that. He answered that a friend of his told him an interesting reason why breaking the glass at the end, despite the immediate response of "Mazal Tov!" actually made some sense.
In short, it is true that we must acknowledge our lack of the Beis HaMikdash and truly express some degree of mourning at its absence during the wedding ceremony. However, once we have had that brief moment of aveilus, that's all there should be - and we jump right back into the simcha of the moment. It is appropriate to feel sorrow, but a person should not dwell on the aveilus longer than necessary, nor be consumed by it, especially at that time. So immediately after the few minutes of Im Eshkocheich (and for some, who don't have anyone sing it, an even shorter period of time) we immediately switch to a "Mazal Tov!" attitude, which does not negate the emotional tug of mourning we experienced mere seconds before.
It's a nice idea, but I don't think I'm chassidic-oriented enough to appreciate it at the same level he did. So my plan is to break the glass during Im Eshkocheich.
What do you guys thing? What practice have you seen the most?