Since noveling season has begun, I've found it amusing that would-be authors are clamoring to tell others about their plots. Many, many threads on the Nanowrimo forums are dedicated to this subject. I don't think this is necessarily a bad thing. I believe it's just a symptom of what anyone does if they come up with their own pet idea--a bit of self-absorption as you will.
I am not immune to the tendency. I would just love to explain ad nauseum about my Nano project. But I've managed to restrain myself for a couple of reasons--people will think me a terrible bore if I spew all of it out here and/or in other forums and nobody in real life really cares all that much about my writing.
Of course no one cares about anyone else's plot (unless they're hard up for one of their own and can't be arsed to invent one whole cloth). They care about stories, which are to plots what countrysides are to maps. Still, you're pointing to a very specific phenomenon: people posting very bad synopses of half-baked plots about which they're still vestigially (and in some cases deservedly) embarrassed, to say nothing of the 'Don't touch, it's mine!' diarist vibe that colours the place (and keeps people from being too specific). NaNovelists for the most part have no idea what the hell they're doing when it comes to long-form fiction assembly; it's no wonder the snyopses are largely valueless.
On the other hand, the exercise of talking about your story forces you to confront its basic value metric: does it mean something to these would-be Readers? If it lands without a sound, maybe that's a bad sign. But NaNo is explicitly about ignoring bad signs of that sort. Serious discussion of plots would be beneficial to everyone, and the 'Let me critique your plot' thread in the Fantasy forum is a prime rubbernecking/gut-check site (because the veteran poster is willing to piss on people's pretensions). But that stuff is discouraged.
I say, don't turn away from such sharing. Deepen it. Making the fora better will make the writers think more (and more variously), and that's a big gain for the community. I'm in a bit of a disenchanted phase this evening, but perhaps I'm just short of sleep.
Well, anyone curious about my plot will know soon enough when November rolls around and I start posting my scribblings up on this site as I usually do.
As for talking about my plot to guage reader reaction--I'm a bit of a pessimist. What's the point of posting it somewhere when no one will respond? I suppose this is just the result of always being talked at and never listened to...