I never keep a written one around unless I am right on the verge of quitting. But the knowledge that I have FU money basically means I always have one stored in the back of my brain.
I've put a lot of detail and thought into some resignation letters in the past, trying to clearly communicate the specific issues with my manager and/or company, but honestly, I doubt I'll do that again. Turns out people don't like being told how they're screwing up. :)
Next time, it'll be, "Had an awesome time here, thanks for everything, best wishes, leaving for something better." Sometimes tact wins over honesty as the best policy.
