What percentage of my salary should be going towards my rent?

I've been reading up on topics like this - one theory I really like is: 1/4 on housing costs (incl utilities), 1/4 on car+insurance, 1/4 on food/fun/health/misc expenses and 1/4 into savings. I think its hard to do, but I've been striving toward this and it seems to work well for me.