Nothing is good or bad in itself as far as I understand; rather it is the intention behind it. So our humor and laughter really depends on what we're laughing at. If we're laughing at another person's pain or making fun of other people in a sarcastic way, then it's not beneficial. However, if it's simply "cosmic humor", learning how to laugh at ourselves and how we often get lost in things can lighten up the tendency to judge ourselves so much.
Simple ways of humor, as Steve often demonstrates in his stories, allow people to accept the truth more easily.
I don't think it's an escape if it's used skillfully or for the right reason. It can prevent us from taking ourselves so seriously as sometimes we tend to do, we get a bit too tight. The tendency to get too tight can be from our idealism and can be released by lightening up a bit.
Smiling? Well, I hope there's nothing unbeneficial about it, because I tend to do it a lot. Sometimes it's just an expression of our caring, of making a connection with others, it depends again on the intention behind it. In this retreat, if you start smiling at all the other retreatants, the intention is usually not so beneficial, because you're not allowing them their space. So it depends on the situation and this goes back again to "Kamma is intention", as the Buddha is recorded to have said. So whether it's beneficial or not we have to look at the intention behind what people do. Is it based in Compassion or not? Is it skillful or unskillful? Is it harmful to ourselves or others, now or in the future?
Humor is something that many of us need to look at, because there's a lot of harmful humor in the world, making fun of other people's suffering. This will definitely not be a benefit to our practice, if we're not able to open to another person's suffering in the appropriate way, rather than laughing at it. So sarcastic types of humor usually are not beneficial in my opinion, because it's often just a mask for aversion. We have to see the energy behind it, like we do in most other things to see if there's a hindrance behind it or whether it's based in good intention.