Grammar commentary

I've just been reading commentary from the linguist's blog and a blog named "Motivated Grammar" about the use of "bad" vs "badly".  The consensus seems to be that "I feel bad" is perfectly acceptable American English, with "I feel badly" also being used, but that we shouldn't worry about the difference too much.  Personally, if I am not feeling well (physically), I say one "I'm not feeling well" - "I'm sick" - or "I feel like c___".  I've also noticed that where I work, they write on the board "so-and-so is ill" not "sick".  Growing up, I would hear "ill" in the sense of terminal illness, or "cranky", "out-of-sorts", "mad".  "Sick" was what we were when we had the flu.