You implied that someone would bring up the fact that dilemma comes from the word "lemma," meaning a proposition, and "di," used as a prefix on Greek words to indicate two of something. The word literally means "two propositions." If you have a dilemma, you have two propositions from which you must chose.
Whether this is used in the context of formal logic or in some more casual conversation, it remains a choice between two propositions. I think you are splitting hairs a little finer than their composition permits by arguing that a misspelling, such as "dilemna," can be acceptable, since the word has such a precise and clear derivation.
As ultimate proof of my proposition: your own spell-checker has flagged "dilemna" as incorrect, and we know that spell-checkers are never wrong! (At the very least, we know that your spell-checker would never be wrong:) )
I am glad to see this in print. I was dozing during the show (dangerous!), so thought I might have dreamed someone thought dilemna was a good spelling.
Additionally, I'll dredge up the old saying, "Fifty million Frenchmen can't be wrong!" While there may be strength in numbers, wrong is still wrong when it comes to spelling and word usage. It doesn't pay to be TOO squeamish these days, but c'mon, people, we've standards to uphold.
Allowing that spelling would be a bumner.
I had a problem similar to the caller with the word for a cone or pyramid with its point removed. Always thought the word was "frustrum", but experts from Merriam-Webster to Firefox's spellchecker assure me that "frustum" is the correct spelling.