Simsi - 5:51 pm on Apr 20, 2012 (gmt 0)
Thanks for the insightful post Brinked.
I'd just like to add an observation re #4 (same server/whois). I used to believe that too but around 10 months ago I had a site that received an oop. I changed several things and one was to move it to a dedicated server which hosts 2 or 3 other sites I run (same whois). They also inter-link but only on very relevant pages.
It's since recovered and is doing fairly well which leads me to believe that there isn't any x-site impact on an oop at the moment. That's not to say there won't be in the future though.