It's been diminishing returns since Dumb and Dumber anyway - that was 1994, by the way - but after seeing Heartbreak so soon after the disastrous "Unhitched," (how can you waste Rashida Jones that badly?) and with approaching projects including a Three Stooges reboot (really!) and a Jonas Brothers movie called Walter the Farting Dog, it's over.
I was never that wild about There's Something About Mary or Kingpin, anyway.
If Tropic Thunder hadn't kicked some serious tail, I would've been very seriously worried about Stiller, too. Before Thunder, do you realize his last good starring role was (depending on how you feel about Dodgeball, I guess) The Royal Tennenbaums? That was 2001. And his part wasn't that big.