It sounds like Best Buy doesn't know how to install these. I got my Zagg at Verizon and asked for the representative there who was the most experienced with protector installs onto curved screens to do mine.
With any protector there seems to be those who either love it or hate it. There is seldom someone in between. I think this is because these protectors aren't as easy to install correctly as it might look. According to the guy who installed mine, the trick with the Zagg is to apply pressure to the flat portion of the screen before and while you are pressing the adhesive edges into place. If you don't they just won't adhere completely. You'll know that even before it pops off because you will likely have sensitivity trouble or see, over time, dust getting under the protector, especially near the edges.
I got the Zagg put on my N8 on Sept 15th. It still looks and works like it did on the day it was installed.