Oliver Steele

Although not a linguist, it seems to me that what is "acceptable" depends on context. Using your example of judgment/judgement, if you are an attorney filing a brief with a court, using the incorrect spelling will suggest to the judge that you are sloppy and inexperienced. Your credibility will be damaged, and your client's case hurt (as a former clerk, more than you might imagine). In that situation, even if the incorrect spelling is extremely common in every day non-legal usage (and even in legal usage), there is an acceptable spelling and an unacceptable one. Of course, in designing a user interface, I could see that it could make sense to use a common, but not officially approved, spelling.