One thing that irritates me more than it probably should is when I've written a whole long response to a comment or post, then I accidentally press some button on the keypad, and the whole thing is gone and irretrievable.
Why is it possible to do this??
And then of course, you just stare at the screen, thinking, "Do I really want to type all that up again?" The thought of it is nauseating. Yet you had something important to say and you don't want it to go unsaid, damn it!
Generally, I end up writing a much abridged version of the original.
I remember I was once in a big online argument with some woman about homebirth, and I made a bunch of arguments I thought were really strong. She replied to me, "I wrote this big reply with all these links refuting your arguments, but it got deleted before I could post it, and I just don't have the time to write it again." Well, you can't argue with that, can you?