I don't truely believe in him, although I've seen various sightings on my singleplayer world. The 'Herobrine Removed' on all the update screens is to remind people that he isn't real and has been removed long ago. Yes, he did stay in Minecraft a bit longer than expected, but that was because someone hacked into Notch's email and kept him in. They eventually found him and he got arrested. So, without a mod or texture pack or anything, I can safely say he isn't real.
