Intelligent design can't be observed because it's unfalsifiable. They point at a flower or animal and say, see, how could that rose have gotten here through all the millenia if the world was just chaos? Clearly it must be the hand of god at work. The clear implication is that everything is the way it's supposed to be, and couldn't have gotten here therefore without guidance, when it's far more reasonable to assume that the way things are is just the result of the way things were.
They believe the existence of roses can't be an accident, and if roses didn't exist they would just point to something else and say it couldn't be an accident. While it's true that an infinite number of things had to go just right for roses to exist now, the same would be true if they didn't exist, or if anything else existed in their place.
The most important aspect of intelligent design is you can't see or test for the presence of the hand of god, and therefore, you can't disprove such a claim. Can you prove there's not an invisible man that you can't hear or touch standing right behind you? No you can't. It's unfalsifiable.
Not to say the theory of evolution isn't perfect, but new evidence arises which supports it all the time, whereas the only way you could prove god's handiwork is if a new species just popped into existence from nowhere.
If god were guiding evolution, than I think it's safe to say that all evolutionary mutations would be beneficial, when most are in fact not because mutations are accidental. Evolution works in that for every 99 useless or detrimental mutations in a species, there'll be one that proves beneficial and therefore is more likely to be passed on to offspring. If god were guiding this, he would have to be pretty shitty at it, which doesn't work if god is perfect, though clearly if he exists he is far from.
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