@Chris ***********
pretty much as Brandon said. It's widely reported that around 6 months using visa exemptions to live here is when you'll start getting questioned by immigration and its exactly when it first happened to me.
After that it just depends, they might ask a couple questions and you're free to go, they might give you a light warning, they might give you a proper warning and flag you in their system and say something like this is your last entry on a tourist visa (or exemption).
What I've seen reported online is that denying people is rare, those that do seem to have been questioned / warned multiple times before being denied. So it really is up to the officer you get on the day.