My opinion on this has changed through the years. Growing up I didn't, it was just an expression people used without thought. When we first moved down here I learned for the first time that people found it offensive, so I just started saying Oh My Gosh in respect to other peoples feelings. Then after I became a Christian I found it offensive because I perceived it as people taking my God's name in vain. But now(still a follower of Jesus) I guess it depends on the circumstance.
I personally wouldn't say it because I believe I would be taking God's name in vain and I would also find it offensive if a fellow believer used the phrase.
But if one doesn't even believe in God or serves a different god, when they're saying it they're not talking about my God at all. So I just recently started to think, should I be offended? They're either using it in reference to a god I don't believe exists or as just a meaningless expression. Doesn't mean I like hearing it, but I guess it depends on the circumstance as to whether or not I would be offended.
Not sure if that I explained that well enough, it's just my rambling thoughts.