I read today that a 17 year-old student who collapsed in his P.E. class and was on life support for four days all of a sudden had his heart start beating again. It hadn't been beating for four days and it started up out of nowhere. One of the doctors at the hospital called it a "miracle."
This is, of course, a pretty amazing happening. There is no particular reason the boy's heart should have started up again. It was stopped and he was being kept alive via life support. The doctor's didn't do anything to get it going again - it just started beating. To some, this is a miracle and some sort of divine intervention. To others, it's a random occurrence and it's stupid to declare it an act of God.
Sometimes I am asked why God doesn't do stuff like He did in the Old Testament (or even the New Testament). There we see things like miraculous healings, pillars of fire, gigantic plagues, and so forth. All sorts of incredible things going on. Some skeptics even go so far as to say if God were to show Himself to them, they'd believe. But because they have no good reason to believe there's a God they don't.
My response to the question generally has two parts. One, assuming that Old Testament times were some sort of miracle-wonderland is a mistake. If you consider the scope of history, the events recorded in the Bible span a very short period of time. Not only that, it is generally considered a record of God's involvement with the world. Naturally it would have a lot of acts of God in its pages. But it doesn't necessarily bother having pages and pages of "nothing that special happened today." So of course the Bible is replete with acts of God - that's the point of it. That doesn't mean that in bible times the Middle East was a land of magic and dragons.
Second, I think God tends to act in ways that will say something to the people at hand. The aftermath of this boy's heart "reboot" is a perfect example. This is a pretty incredible thing. It's not supposed to happen and there's no good explanation for why it did. To some this is proof of God and to others it isn't. I tend to think any sort of "miracle" God did to prove Himself to a particular kind of person would always meet with skepticism. If you're committed to a naturalistic worldview then everything will happen via natural means. Even "unexplainable" events cannot be considered evidence of the supernatural - the naturalist is more comfortable saying "things just happen sometimes" or "I'm sure there's an explanation for this."
As an aside, I do think it's just as silly for a theist to say "we can't explain it, so it must be God!" And I tend to be on the skeptical side when people say God did things.
My whole point here is this - and it's nothing particularly new or profound - but to some, no evidence could ever be enough to suggest there is such a thing as God. Now, some people don't require any evidence at all (which I believe is a foolish way to go about things). But to demand God perform miracles or expect them is, in my view, a bit of a copout when it comes to reasons to be an atheist. You'll probably find another way to explain it anyway. Also, I do think God still does miracles. But I think He saves them for the people with whom they will actually have an impact. And I think we are probably surrounded by miraculous occurrences every day that we have no idea about. I just don't feel comfortable identifying them.