I've noticed that my carrier (Vodafone UK) sometimes appears in the status bar at the top left. When is not there does it simply mean I'm getting poor reception?
No. Not at all. I'm on sprint in the US and it does the same thing on mine. Sprint pops up on the top left when nothing else is there. It has nothing to do with reception.
I've noticed that my carrier (Vodafone UK) sometimes appears in the status bar at the top left. When is not there does it simply mean I'm getting poor reception?