[tomw2005]

I was not meaning to equate ArXiv to Nature. I can see how I implied that though.

As I've said in another comment it was used much more frequently during my undergrad years than at postgrad. Within Maths and Physics it is generally trustworthy as they are pre-prints of papers to established journals.

Would I cite an arxiv reference in a paper for submission or thesis? 99% of the time, no. Useful for citing on the web though where your users may not have access to the final journal article behind a paywall.