In Poland it scales over time: you start off with 2 weeks notice (for both sides), after a year or so this jumps to one month, and after 3 years it jumps to 3 months, or something like that. I've seen people quit right before their 3 year anniversary just so that they don't fall into the 3-months-notice period.

I haven't worked much on regular job agreements (been contracting or "contracting" most of my life), but generally if you want to quit you go to your boss and say "hey, I wanna quit" and you negotiate when, regardless of the default requirements (which only come into play if either side doesn't agree). There's no business in keeping an unproductive employee around for 3 months.