The folks working on the official PHP Documentation have done a marvellous job in providing a mostly easy to follow documentation, with good examples. However, as with anything, there can still be some improvement. I see two shortcomings and these have to do with structure rather than content, and I think the community can help solve them.
There's two things he suggests can be done to help refine the documentation process, including a move into a more wiki-style environment (with the content under a fully open license). Specifically, he suggests making a move to Wikibooks to encourage more participation from the PHP community.