Go carefully with contacts you find via GR is my advice.  When I started on our FH, I used GR and was contacted by someone whom I knew was related to us.  He 'lifted' all my stuff with no 'may I?' first, including many of my errors which I have now corrected  on the tree on my computer!  I have watched his tree on GR over the past 3 years, and have seen it go from 15 people, to 50, to 5,000 in a matter of months ... accurate ?   I very much doubt it !  
FH on RootsChat is a much more civilsed matter ... give and take, help freely given, friends made.  What more could one want ?