I used to think largely as you do, Brad. But I've come around. (The autobiography, for those interested in the demographics of this term use: I was a child Christian and theist, then a college-student athiest, and now a young-adult agnostic (who, incidentally, studies epistemology).)

In abstract terms, there's a clear place for a middle ground between believing something and disbeliving it; sometimes, we think there's no good reason to believe either way (or equal reason on both sides), and suspend judgment. The Iranian government says that a group of British sailors was captured in Iranian waters, something the British deny. Jack believes the Iranians; he thinks the sailors were in Iranian waters. Danny disbelieves them, trusting the British instead; he disbelieves that they were in Iranian waters (that is: he believes they were NOT in Iranian waters.) I look at the situation and decide I don't have enough evidence to tell one way or the other. I don't believe it, but I don't disbelieve it either. I suspend judgment.

Once we admit that there is a category of suspension of judgment, there's an obvious place for agnosticism. Is there a God? Theists believe there is; atheists believe there is not. Agnostics suspend judgment. We don't think that we have good enough grounds for believing one way or the other. (We might, but needn't, add that we don't think anyone else has such grounds either.)

Some atheists will press us on this: "if you believe there's no good evidence for the existence of God, you should just believe that there is no God! What better reason could there be for disbelief? (This is, after all, why we disbelieve in fairies!)"

The atheist may be right in pressing this argument -- but he is arguing on substantive grounds that we should be atheists instead of agnostics. He's not arguing that there's no category that we occupy. And indeed, there's room to question whether his argument is cogent. I used to think it was, but now I think it may not be. He's appealing to some principle of ontological parsimony or Occam's Razor or some such thing. These are substantive principles about rationality. They're extremely popular and widespread principles, but they are substantive ones, and I sometimes worry whether they hold up to philosophical scrutiny. Why must we think there's no God, once we admit that there's no conclusive evidence for God's existence? Why not just suspend belief about God? Maybe about fairies too! Maybe you think this is just crazy. Maybe it is. I don't want to get into an argument on the merits of agnosticism here; the point is just that there is a view to be held, and that it's not absolutely nuts to hold it.

Perhaps an analogy will help. Here's a case where most people will agree that the parallel to the agnostic line is right. There are a whole bunch of stars in the universe; consider the claim that, at this very instant, there is an even number of stars in the universe. Perhaps someone will try to convince us that there are. We will demand evidence, and he will be unable to supply any. No one thinks that the proper response at this point is to believe that there is an ODD number of stars; the rational thing to do is to suspend judgment. The agnostic thinks that "there is an even number of stars" is, in the relevant respects, like "there is a God". The athiest thinks there's an important difference between these two cases.

I hope that clarifies the position and gives some plausibility to it. I don't know that I can meet the challenge given, but I think it's unreasonable:

I challenge proclaimed agnostics to describe how their life is different from those who say there’s no god

To see that this is unreasonable as a test for there being a significant difference between athiests and agnostics, consider: how is the life of the person who believes there is an even number of stars different from that of the person who believes there is an odd number? How is each of them different from the person who is agnostic about that question? No answer is obviously true; the only test distinguishing them might be to put the question to each. But there is an epistemic difference. Indeed, we think that one, and not the other two, is responding rationally to the evidence.