I just got shown this very interesting artical by Ken Rockwell about the use of apeture and its effect on sharpness, where a smaller apeture produces a sharper image and that an apeture of f8 or wider should be used for maximum sharpness unless depth of field is absolutely necessary.
I don't know if other people know about this already (I may just be lacking in knowledge ) but thought I'd share and see what peoples thoughts were.

Here is the artical:
http://kenrockwell.com/tech/unsharp.htm

And here is another artical from someone else:
http://www.cambridgeincolour.com/tutori ... graphy.htm