I agree with Tooltime's claim that essentially everyone is agnostic in the sense that there is always a measure of doubt in each belief we arrive at, but I think that should just be obvious to people. I also agree that there are definitely people who call themselves agnostic who are actually atheists. In fact, most atheists are agnostic-atheists (just as most theists are agnostic-theists - hence the faith). The only reason I don't label myself as such, even though my views about the metaphysical make it an accurate label, is because I feel like the term is too easily misunderstood.
And ultimately, as Tooltime says, telling someone you're "agnostic" doesn't really mean much. Agnosticism covers the entire spectrum of belief and I feel like whatever assumption you live your life on (whether god does or doesn't exist in this case) is what your religious identity should be. I know this seems like a silly thing to even bring up, but since there is such a big discrepancy between the amount of people hold atheistic view points and those who are willing to call themselves "atheist" I think this is an important issue.
If you are still unsure about agnosticism or would just like to know more, I would definitely recommend starting with the wikipedia page for agnosticism. It's one of the more informative ones I've read.