This is what I also thought until one year ago. Now I have several real paradigms where backlinks from OFF-topic, high PR sites count significantly.
It all really depend on what we compare:
<high PR from off-topic site> VS. <low PR from on-topic site>: Winner = OFF-topic
<PRx from off-topic site> VS. <PRx (equal) from on-topic site>: Winner = ON-topic
A cool mix will bring you the best results for sure :)
[edited by: aris1970 at 10:31 pm (utc) on June 28, 2005]