So I was reading the Bad Astronomy Blog today and I came across a post with a link to this: http://www.rinkworks.com/words/confused.shtml
I didn't even know Adjure, Luxuriant, Flack, Sanguinary, Peccant, Insolate, or Chaff were words, and although I knew the meanings of "Discrete and Discreet", I didn't know they were spelt differently. Opps.
I think most of the people on this forum (and all others) could stand to take a good long look at that page, and other pages like it.
I think I'll try to find a page that specifies the uses of simpler words like "There, Their, and They're" as well.