Some of you may already know who Ken Ham is; if not you can read about him here.
One of the videos Ken Ham has produced to defend the account of creation in Genesis has been critiqued here.
Of the things I've read of Ken Ham's his "Were You There?" article is probably the piece that has provoked the most thought.
My initial reaction to the article is this. Say I wake up some morning and I look outside and there is snow on the ground. Well, I didn't actually see the snow fall, just as I have never witnessed the billions of years of stellar, biological, etc. evolution, however, I have seen snow fall in the past, just as scientists have witnessed various acts of geological, etc. change since the 19th century. So, why would I assume this particular snowfall was any different in its creation than past snowfalls I've witnessed? This prompts an allied question - why would the way that snow is created long ago be different than that it is today? And of course why would the geological, etc. processes we see today be different in the past?
So yeah, I wasn't there. But the clues that exist in current patterns of change in combination with the historical record (e.g., rock strata, the genome of a particular animal, fossils, etc.) allow us to make powerful and convincing inferences based on that data.
Addendum: In the critique of Ham's video I found the bit about the advent of nylon metabolism to be a major "wow" point. Namely that nylon did not exist prior to 1935 and yet bacteria which eat nylon have come into existance. Sounds like evolution to me.