Have you ever posted to a thread and then continued onto other threads. A while (A couple hours/days, whatever works for you) later, you think [i]Shouldn't they have replied by now?[/i] You head over to your subscriptions and find that it isn't there. Your a very active person, and there is a ton of your past posts to search through to find the correct one. 

Wouldn't it be useful that, if you are replying to a thread the first time/creating a thread, there would be a little dialog that pops up and asks if you want to subscribe, or at least if there were a box next to the post button that you tick if you want to subscribe. Maybe even a drop-down arrow asking what kind of notification you want (Control panel only/daily update/weekly update/etc).

[size=1]The fine print: Not that I need this, it's just something that I thought would be useful for the more active people. (Sorta like me last year.... before grade 11 happened...)[/size]