I sometimes choose to subscribe to threads on the phone that I haven't posted in (to remind me to do so later on the pc or iPad). Which brings me to my other point, if you are using the mobile version of the site Ixi then you won't have a subscribed threads feed (though threads you've posted in...
You can always use the search function periodically to check if someone was talking/quoting/mentioning you. I do (I search for Kern* so I see lot of stuff about popcorn and such too :P)