Patri Friedman at Catallarchy gave some excellent advice on arguing (from some reading he's doing on Ben Franklin):
When another asserted something that I thought an error, I denied myself the pleasure of contradicting him abruptly, and of showing him immediately some absurdity in his proposition. In answering I began by observing that in certain cases or circumstances his opinion would be right, but in the present case there appeared or seemed to me some difference, etc.Click here for the whole thing.
He's on to something, particularly in the academic world. All too often, we have a tendency to take each argument as a one-shot game. So, without humulity we try to win the current argument at all costs. Unfortunately, this is counterproductive both in the short run and in the long one.
I'm a bit of a "conference rat" (I've averaged better than two conferences a year for the last five years). I've seen a lot of work presented over the years that was seriously flawed (some of it was my own). Sad to say, but I wasn't a very good follower of Franklin's advice early in my career. As a result, some of the people I made comments or suggestions to not only didn't give the comments a fair hearing, but they also were less likely to want to share a drink with me after the presentation. While I'm not the brightest bulb in the lamp, I am teachable, so I eventually learned better (mostly due to good advice given in Franklin's style). Once I loosened up, I not only found people listening to what I had to say, I also found myself with a lot more people to hang out with, and both are good things.
One of my grad school mentors (I'll call him Dr. Jones) was notorious for the way he would ask questions/make comments during presentations at our school. Near the beginning of a presentation, at some point he would typically scratch his head and look mildly puzzled. Then he'd start out by saying something like, "I'm sure this is me, and I'm just missing something. But, it seems to me like.... Could you explain to me why...". At this point, he's ask a question that typically cut to the heart of the matter.
It was so effective (and fun to watch) because he was always polite and non-confrontational. It was kind of like seeing an academic version of Columbo (without the sloppy appearance - Jones was a very stylish dresser).
To this day, a couple of my classmates call this style of questioning "pulling a Jones". Sometimes when we're in a presentation, one of us will start scratching his/her head just to get a smile out of our friends.