A while back, Peter Stothard of the TLS wrote on his blog that we had the apostrophe in the wrong place for our Bookaholics' Guide to Book Blogs.
Although I replied on his blog that I thought we were right, I have had considerable self doubt on this matter of apostrophe's ever since. However, we just had our reminder to update our entry for a well known guide book to the publishing industry - and it is called (have you guessed?)
Writers' and Artists' Yearbook
So now I am pretty sure I was right.