Back in June 2014, when I first built my Printrbot Simple Metal kit, like many people,I had a lot of problems with adhesion of print objects to the bed even when using blue tape cleaned with alcohol. When a heated bed modification became available, I bought one and my print success rate went up tremendously, and now my problem is that I have great difficulty in getting parts loose from the bed, especially if it is something more than a couple of inches across. I have acquired a 3D Print Removal Tool from ToyBuilder that has really helped get stuff loose.

Even with a heated bed, I still had problems with pointy parts of a print wanting to curl up, and sometimes knock the print loose when it would impact with the extruder nozzle. I finally figured out that it was two things causing that.
1. I had a ceiling fan causing a draft on one side of the print bed, but not the other.
2. The Simple Metal has one fan mounted on the left side of the extruder. It's airflow to most of the right side of a print is blocked by the extruder and Z end stop detector. Unequal airflow was causing the unwanted curling.

I've learned to keep small pieces of paper to use as air dams handy so that I can tape them to the bed to make the air flow evenly over the whole print. At one time I seriously considered building a heat chamber, but now I feel it is unnecessary.