It hasn't hurt mine. The lithium-ion battery does not suffer from the memory effect of earlier batteries. However, Apple does recommend that you discharge it once a month. Here is everything you need to know about iPhone batteries" http://www.apple.com/batteries/iphone.html
Personally, I keep it connected to power in the office (a good part of the day) and in the car. That's fine, as long as you run on the battery occasionally (which is necessary as lithium-based batteries do need to be used to maintain their health).