Apparently, the basics of philosophy are lost on some Sophistic boy-children around the internet. I figured I'd clear something up here. Of course I'll potentially be called dumb or arrogant for doing so, but such is the penalty of speaking the truth, I suppose.
One of the first things you're supposed to learn in logic is different argument forms. One of those forms is the argument from analogy. It is one of the less precise forms of argument, but used the correct way it can be a powerful tool.
William Paley came up with one of the more famous arguments from analogy, the watchmaker analogy. Paley posited that if we were to discover a watch, we would observe its complex movements and parts that are in specified places in order for it to function. We would never attribute that to blind chance, but would conclude that someone designed the watch. Likewise, we can see other things with complex intricacies which seem to necessitate an intelligent source.
Now, obviously the argument from analogy is never a perfect science. Things you compare are never identical to one another, otherwise they would be the same thing. Rather you notice that the things are similar, and as such have the same kinds of properties or operations. It's never a perfect match. So if someone says about Paley's argument, "well, the watch has gears and hands that tell time, but this cell (or eye, or universe) doesn't and works differently than a watch does," it would be a terrible way to refute the argument. Of course we know that every aspect of a watch is not going to relate to every aspect of something else you are comparing it to to infer design. The point is we are taking one thing that we know is designed and pointing out that another thing has similar complexities, therefore that thing is designed. It's never a perfect match, but it's not meant to be.