I suppose this would depend a little bit on age, but in general - what times should someone hit in order to be consider a good runner? How about very good?
I first started running a few years ago (I'm 31), and I find that it's a constant moving target. What I first thought was good (below) now looks 'meh'...
Mile - under 5
5k - under 18
10k - under 38
Marathon - under 3