I've heard people in front of me say "I believe" before. More often than that I've seen people say nothing. (I don't think it's beacuse they are used to the Latin Mass- most likely it's because they had their mouths full of chewing gum.) The worst though is when they grab the Host out of the priest's hand.
Yes, it can be disheartening to see these abuses. And the sad thing is that the priests can re-educate their congregations and solve the problems! (Or at least some of them.)
I know things have changed, but even this lapsed Catholic is shocked that people touch the Host. {{{shudder}}}
I saw a man take the host from the priest's fingers, and then as he was walking away with the host, he tucked it into a plastic bag and put it into his pocket. I told the usher about it and he didn't believe me. Another usher said that when he was trained for (Ordinary) Eucharistic Minister, they taught the class that when a fragment of the host falls to the floor it's not important because a crumb or piece small enough that it's hard to see whether or not it is a fragment "loses its character."
That same priest faced another man who knelt for communion but the priest told him to stand. The man just knelt there with his toungue out, waiting, with the single file line of people behind him. The priest finally placed the host on his tongue, but as the man rose, the priest said to him, "You're a big help." The communicant would have had to speak with his tongue occupied in order to answer.
One mother was in line behind her daughter, and when the girl opened her mouth to receive on the tongue with her hands in a prayerful vertical posture, her mother reached around the girl, grabbed her forearm and thrust it forward toward the priest, as if to encourage her to take the host in her hand, instead.
As an observer I've seen at least one abuse every day at such Novus Ordo places. But in years of observation, I have yet to see any abuse at a Traditional Latin Mass. Whenever I asked a N.O. priest about the abuses, he gave me some excuse and changed the subject. When I've mentioned this to a TLM priest, he usually says something like, "It sounds like you should have no problem deciding which Mass to attend."