Verizon not having Roll Over like AT&T effectively means you can not use all your data due to fears of going over the limit.
With AT&T one develops an extra data buffer so to speak. Not with Verizon. And if you go over, it's $15 per extra GB.
This is really a big Verizon-Negative in my opinion. Would be nice if the FCC could intervene or maybe even Verizon would just 'do the right thing!'