Speaking from experience on the MDX site, I can tell you that the kbase becomes and invaluable resource as time goes by.
The Problems Forum is appropriate to identify & discuss problems and their solutions. The challenge is that 6 months from now, the "my glovebox rattles" thread will drop into oblivion. Newbies (or people with a similar problem that is just appearing) will do a search (if we're lucky and they don't start a new thread) -- and it'll turn up multiple threads.
The kbase is a great repository for the problem+resolution in a single place.
It provides a link to the discussion(s) if the owner is inclined to see all the Sherlock Holmes in action
For example, on the first-year MDXs, there was a suspension "thud" going over bumps. Several seperate threads and hundreds of posts ensued. If you newly acquired the thud on your car, would you rather read through the several threads and hundreds of posts, or just go to the single entry in the kbase that says "Suspension Thud" as the problem and has a couple of bullets for the solution?
I'd suggest making entries into the kbase when a potential resolution is actually found (sometimes the resolution is "it's normal" - like with the wind buffeting/roof vibe thread). Posting a problem without a resolution in the kbase begs for discussion on how to fix -- and the kbase isn't good for that (it's not set up for threaded discussions, and people don't check it daily) -> that's what the forums are for.
OK, off the soapbox