I am a loud person, I ask lots of questions during lab meetings, I ask lots of questions during group meeting. I always make a point of giving feedback on the overall presentation to the presenter that is specific, not just saying "good job". I do these things because I think the best part of science is the dynamic interchange between smart people about cool ideas and problems. I think lab meeting is for brainstorming solutions to problems. Sadly, in most of our lab meetings my PI and I are the only ones that ever say anything.
Also it really really sucks when you spend hours preparing a presentation and then are greeted with total silence and blank stares when you finally give it.
Anyway, I got a really nice email from a graduate student in our lab thanking me for my feedback and ideas and letting me know how helpful he thought my comments were during yesterday's lab meeting.
It made me feel all warm and fuzzy inside.