I think that 10 might be a bit too much. I do find myself always looking for at least 1 more level and possibly 2. So my vote is for at least 7, and 8 levels deep would be more than enough in my opinion.

I would love to see an admin option for this one. By default, I think 5 levels is great, as it forces you to think about your heirarchy when you are building it. After you grow into your HelpMaster shoes, though, you may want to expand this. At this point an administrator could decide to open it up further to (x) levels. 

With that in mind, I personally wouldn't like to work with more than 6 or 7 levels at most. It would get so fastidious. It might be great for reporting, but it would be unworkable in the real world.

Also, it would have to be treated with care, as increasing levels would be simple enough, but decreasing would be a different can of worms if, down the track, it was decided that 5 levels were enough after all.

Scott