I'm almost at the end of my permission to stay in Serbia legally. I've heard stories that people went over the Bosnian border and then came back to Serbia during the three years period (UK nationality). They might stamp the passport or not. But they didn't check the old stamps if overstayed.
My personal view of it all is that the border crossings do not care at all. But airport checks. And that if you do it the legal way, it will be more problems going through their bureaucracy.
Someone else has some insight if this could be possible to overstay during a long period of time? What could be the consequences?