I write semi-fiction a lot. But just like DeadReligion said, it's never less than about 20 pages. It seems like a lot, but when you've spent so much time on it, and you really have the feeling for it it kinda flies by.
I also use a lot of description in my writing, I'm a little like Steinbeck in 'Of mice and men' at the start of each chapter he'd have a page or two of description. That's because it was originally written to be performed on stage though, the description at the beginning of each chapter is like the introduction and setting at the beginning of each scene or act in a play.
Would certainly be good fun to read some other peoples work though. As you've said, just leaving comments and stuff instead of full crits.
Timmy P