I actually know multiple people who gave >3 months of notice in the past. They were trying to be considerate professionals. In return, my employer used the opportunity to treat them as badly as possible for the remainder of their employment in nearly every case. One guy was recently given "double duty" for his last 4 months . . . he complained about it, but why he didn't just refuse to do it is beyond me. Now that I think about it, they also tried to do that to another lady who was leaving with a lot of advance notice a few years ago, but she told them to stuff it in a lot more words (in an email that I was copied on . . . should have saved that for its comedic value.)
Gah, should I advise those close to me here who are thinking about leaving to give the month notice if they can--to get what my employer thinks is the coveted "eligible for rehire" status--but then plan to take vacation and personal days for most of it? Lol, that's probably the way to go.