I simply click on the rep button when I've found a post particularly entertaining, interesting or when I want to say a virtual 'that was great.' Although I have to admit sometimes I'm so carried away with what I am reading that I don't always click on the button, or remember to go back and give someone a point or two when I get one of those 'you need to spread some rep around' messages. Which makes me feel bad...
I have never given a bad rep point, and I hope I won't do it. I rarely see a post which I find 
that bad. If I don't like what a post says, then I 'change the channel', so to speak. It would have to be incredibly offensive for me to give out a negative. Case in point, we have a discussion board at work, which obviously must adhere to equal opps policies, and I have on one or two occasions found something to be most offensive, but I just post explaining why I find the person's point to be disagreeable - even this makes me feel a bit guilty at times. One thing which I do avoid is pulling people up on their use of English, as I do not know that person's circumstances; as an example, some of the technology used to convert braille into text does not always pick up on spelling errors. 
It's a good system though, and I would like to add here some warm - and not at all toady - thanks for anyone who has given me points - it's not something I expected at all, as in my experience forums can be cliquey and these things can be awkward - to my delight the Downs is not like that at all, and that's why I spend so much time here!  
