I hate it when you have, say, a bit of great news and excitedly tell someone, only for them to tell you you've already said.
Or worse, when you tell someone and they're all suprised and excited for you, and you remember later you'd already told them and they'd been pretending to save you the embarrassment 
Obviously some general advice on MN on things like physical abuse are pretty universal, and it can be helpful to post something that's happened to you lots of times if it helped an OP out of a difficult situation.
But I saw an OP a bit back being told by a poster that she (the OP) had asked a similar kind of question about 4 years previously 
The OP was a bit taken aback, but the other person had some kind of freaky photographic memory rather than being a rampant stalker.
Even though most posters don't notice MN names (which I don't believe 
) and there are squillions of us on here (disregarding the MNHQ personas 
), it's not the first time I've seen somebody being picked up for repeating themselves.
So how many times can you post the same experience/opinion before you're considered banging on?