Well it is not as easy as simply staying. I am going to Sao Paulo on wednesday, my 88th day. and something like my 170th in total. Obviously I want to come back and stay another 3 months a week later. So I am interested in the buzz on that topic as well.
Also, one big difference I see between overstaying and risking re-entries:
Overstaying, you are clearly breaking the law.
When you leave the country every 90 days, you are in a grey zone. What you are doing is not perfectly legal but as long as they give you your stamp it is not ilegal either.
Obviously both have their ups and downs, but I prefer the second one since I am not totally f***ed if they don't let me in (eventhough it would really suck of course).