As a reader, I'll post FDK that mostly consists of.. um.. gushing.
Or all these really silly things that go through my head while I'm reading something -- usually not concrit at all, just things that I feel like saying and will generally amuse (or at least, I like to think it will). Something that'll let the writer know I laughed at this or that, that something made me smile, that something else brought tears to my eyes... you know... it's not concrit, but it probably lets the writer know where they hit the spot.
If I see typos or blatant errors, I won't leave them in an FDK thread, I'll send a PM instead.
Concrit, I'll usually do in beta. That's what you expect of a beta, anyway, right? Or at least, that's what I would expect of one of mine, so...
Now, as a *writer*, I like every piece of FDK - no matter how big or small. Just knowing that a story's been read and appreciated is wonderful. It's immensely encouraging. Sure concrit is useful, and I will personally consider it no matter who it's from, but even a "good work!" is really appreciated. And if you want to point out what you liked, what you were thinking and you feel like making silly comments in your FDK, you'll have this slightly nutty fangirl giggling and clapping as she reads it.
