Intelligent design does not necessarily mean
perfect design - after all,
humans design things intelligently every day, but none of it is
perfect.
However, you have to take into account the designer. If the designer is said to be perfect, for example, God, then the creation itself would have to be perfect. A design that was less than perfect would imply that the creator was also less than perfect.
Of course, perfect means perfectly designed for the desired task/goal, so some things that may be considered flaws may be due to using the item designed for a different purpose than intended.
But given that this was written in relation to the creationist theory of intelligent design, the lack of perfection in the human body, as seen in little things that appear purposeless and jury-rigged, go a long way toward refuting such a "theory".
Now, it's fine and dandy to discuss whether or not the appendix has a purpose, and that maybe it's not useless. However, there are plenty of other parts of the human body that can't seem to be anything BUT flaws. For example, the urethra in a male goes right through the prostate - a gland that is very susceptable to swelling, and thus blocks the urethra. Or the "funny bone" - a nerve that, for no reason, runs on the OUTSIDE of the elbow, making it very easy to hit it on something.
There are plenty of other examples in other species that have no purpose and no explanation other than jury-rigged design due to evolution.