I eject mine all the time just for the Hell of it. More times than I can count. No ill effects yet.
It's a Silicon Power 64GB Class 10 MicroSD in a Generic Chinese SD adapter. Had it sometime since the begining of this year.
I've had that happen but never witnessed it breaking, have you? I'll go to pick up my SD card and suddenly the edge has broken away, seemingly without any actual trauma. I imagine it's cheap plastic. Haven't had that happen in a while though.
I belive Thomas is talking about full-size SD having this fault. I have never had a Micro-to Full SD adapter break on me.
I've never seen an actual SD break, but I've seen adapters break quite frequently. If you plug the microSD in too far, it slowly wears down the plastic and/or acts as a lever pushing the top and bottom halves apart.
It can damage the pads so the connector can't make electrical contact, but you can fix that with several pieces of electrically conductive tape.
Image from Google, not mine
If you pull it out before all the data is written, you'll damage the filesystem and have to reformat. That doesn't damage the actual card, it just corrupts the data stored on it. And it happens instantly, not over the course of several times.
It prevents the system it's installed in from writing data to it. Effectively making it read-only.
It's a physical switch that the computer can read the position of. It doesn't actually protect the card, and the computer can do whatever it wants with the data, but it means "The person holding this card would appreciate if this computer does not write any data."
Those are most likely impressions of the pins from the reader inside the 3DS. Wear that is inevitable and should not hinder connectivity.
