I don't want to go in on either side of the debate going on but I have to question this. I've never heard anyone suggest the word gay is offensive. There's plenty of other words which are used to insult gay people but gay isn't one of them. I mean it's one of the words in LGBT you know.
Woop. This is one I have a bit of authority on.
Context is important here. "Gay" used to describe someone's sexuality is not offensive at all. "Gay" being used as an adjective to describe something negatively or flamboyantly is... complicated. Just as the "n word", "c word(s)" etc. is complicated.
One thing a lot of people who fit in with the majority (male, white, middle class etc.) get uppity about is that "they get to use it and we don't". There is a maaaaaaaaaassive reason for this. If you're ever in a position where you are in a minority group and the rest of the room is a part of the majority, and they use these words easily, you get incredibly uncomfortable. If a gay person is, say, in a boardroom with 5 other people, and the other people are comfortably throwing the word "gay" around ("your suit is so gay" etc) then you really do feel uncomfortable. Without knowing more about these people, they could be anywhere between homophobic bigots to gay activists. The problem is that since you don't know what their intentions are, you don't know how to construe what they say. Now, if one of them revealed that they were gay and were making these jokes, it clearly removes any chance of what they were saying being done out of malice. They can't be gay and homophobic. But if a person reveals that they are straight and still say these things, you still have no idea what their intentions are. It could be disparaging, it could be friendly.
I'm bisexual and have straight friends that make these jokes. I'm comfortable with it because I know these people very well. I know what their intentions are when they make these jokes. If a person I didn't know made exactly the same joke, I'd feel a little put out by it. Which is why making these jokes in public, on tv, on forums etc. is nearly always a bad idea.
Also, the reason gay people DO make gay jokes (as black people make black jokes etc.) is because it de-powers these words and feelings. The idea is to remove the connotations and stigma that these words have had over time. And it's working! Kids are showing a greater degree of empathy towards minorities over time. Racist and homophobic language is used less in schools, making the schools a lot more inclusive. As is the workplace. Homophobes and racists may still exist, but they now have to hide it. It gives more power for minorities to be themselves. It's the real success story of the "PC brigade".
edit: A bit of advice and a cautionary tale for teenagers on here. When I was a teenager, I didn't tell anyone that I was bisexual simply because people made "gay jokes". When I made friends with someone who didn't make these jokes, I did tell them eventually, and it did get out to everyone else. What I found out was that the people who made the gay jokes who I didn't tell earlier, were actually completely fine with it. Their intentions weren't to put out gay people. But in these matters, it's about the listener's perceptions, not the speaker's intentions, that construes whether something is offensive or not. I felt uncomfortable because I perceived homophobia, not because people intended homophobia. This is completely normal, you don't want to be coming out to people you would perceive to be a threat. By being PC and not making these jokes, you construct a much more comfortable atmosphere for people to be themselves.