TheMadScientist - 9:58 pm on Nov 27, 2012 (gmt 0)
Definitely what goodroi said...
I've personally seen #1 (especially with .htaccess files) totally, royally, mess things up and #3 is something I see often, because it seems many people only like to improve things when they're not working rather than working to make sure they stay a-step-ahead constantly. (I may have gotten a 'Been there; Done that' shirt for #3 a few years ago myself, but now I think one of the biggest things to do is keep pushing ahead harder when things look good.)
I also totally agree about not looking at the rankings too much. I've moved much more to traffic and indexed pages as signals than worrying about what varying degree of personalization I'm going to see today.