Never played with this option but I had a user asking how he could hide forums he wasn't interested in.

Under Default Starting View I see these two options:

My Watch Lists

Traditional Forum View

He is watching specific forums, but after changing to "My Watch Lists" he still sees every forum upon log-in.

Am I missing a step?

Watch lists are just a way of tracking the forums you want to keep an eye on. (Almost like bookmarks.)

It might be easier for your user to click on the little arrows at the top right of each category - they will then close that forum and remember their status for his next visit.

Thanks, I did notice that when poking around while logged in as him.