I may be dangerously close to foot-in-mouth syndrome here, but the idea as I see it is that watched threads consists of all the threads you're interested in, and TIO is obviously all the threads you've posted on. If you're interested in a thread and have posted in it, then surely you'll also be watching it? Similarly if you're not interested in a thread you've posted on you can unwatch it (or even hide it). Do we need this level of customisability for TIO? On most forum programs the concepts of watched threads and threads posted in are basically the same thing anyway.
I'm not sure what's happening with the thread hiding, it seems to be working for me. Are you properly logged in, i.e. you get Log out/Inbox/etc. links at the top of the page? And do your hidden threads appear in the last hour/last day pages too?
Don't worry, I'm not ignoring you. Just trying to keep my forum posts from becoming full-blown essays. Too much of a good thing, or something like that.
~D