I was always completely comfortable with this word until I ran across it today while copy editing a sentence that started like this:
"Now that you’ve ascertained that the ocean-view room you reserved does indeed have an ocean view ..."
To me, "ascertain" connotes a somewhat lengthy and difficult process of investigation -- like you have to work a little to find out what you want to know. So it seemed a bad word choice in the sentence. I mean, to find out whether your hotel room has an ocean view, all you have to do is look up or maybe take three steps toward the window. I wanted to change "ascertained" to "confirmed." But first I looked it up.
From American Heritage at dictionary.com:
ascertain. To discover with certainty, as through examination or experimentation. See Synonyms at discover.
Ignoring my gut feeling, I left the passage unchanged.