I experience this effect very strongly as well. I'm basically incapable of writing without some form of interaction, and since I have not found anyone with whom I can write collaboratively so far my writing has been constrained to things that work well as forum games/CYOAs/other suggestion-driven fiction. So yea, some kind of collaborative setting with other LWers to solve this problem would be nice. I've tried a few times to get such started but they tend to fizzle out.

Random note: this is also basically the reason why Eliezer started blogging if I remember correctly.