My mother, a passionat grammarian, has explained to me numerous times that it is actually proper to say "I feel good" rather than "I feel well" (although people think it sounds classy to use 'well') since "I feel good" means "I feel healthy" (good and healthy are both nouns) and "I feel well" means "I can touch things well" (well being an adverb). The negative usage is the same (I feel bad = I feel sick...and I feel badly should mean I don't have a good sense of touch). However, the whole thing is a moot point since English follows usage and people now commonly use well/badly. Even though I know it's not proper grammar, I will often say "I feel well." Or, if I'm around my mother, I can avoid it all together and say "I feel healthy" :)