Tom, since ADMIN call this a diary area, I would have thought that it would work like a physical diary. Each person was one diary page and they post what they are up to at the moment.
I personally think that the post that DanB has been doing with the building of the new windmill should go here while anything that is a question should go on the discussion side of the board.
If I kept a real physical diary, I would expect someone else other than me to put entries in it. Now other people may have comments, questions or just bravos about anything posted in someone else's diary but that, I think, should be kept physically separate from the diary itself.
Now to keep things practical, when you select someones diary, there should be a limit on how far back it fetches on one page but something could be worked out.
Look at the weblogs (blogs) model. That's how I would like to see the diaries work.
Martin.