One more idea...
How about an automatic e-mail to the OP after say 20 posts or two weeks of inactivity in a thread, saying something like:

"Did information in this thread help You? If you received useful information, please consider adding it to an existing wiki page, or create a new one.

You can find the wiki under http://wiki.maemo.org/Main_Page"

Optionally extended by:

"A wiki search for this thread's subject resulted in the following list:
...
"