Is there any harm in using a USB data cable of any other phone (say LG) for charging up a Nexus S? "Any harm" here means will it adversely effect my battery life or the Nexus S device in any way?
USB data cables are pretty much interchangeable. Even on devices that have modified sockets to allow connecting a headset cable to the USB port, you can usually still use a normal USB cable for charging and data with no harm to the device.
As far as I know, Nexus S uses the so called
micro-USB cable, the same my Galaxy 5 does.
This is very good, because you can buy a generic cable like that in retail stores or shops that sells electronic stuff. I did so a few days after I bought my cell phone, and it costed the equivalent of US$4.00 in my country (Chile).