Something I've been finding more and more which I've attributed to the growing data centers for all SE's (Google especially) is location.
I'll get a client (and it doesn't matter where they are from Japan, US, Canada, EU etc) call saying we lost our rankings!!!! I'll query and they are right where they were. I get them to do a tracert and they end up at one IP I'm at another (google.com) with different results.
I've tested having them change their DNS settings to use the google IP I was showing good results at and they get the same SERP's I did.
So there really is something to it. If you find bad SERPs one moment tracert it and copy down the IP.. when you get a good SERP see if that IP isn't different, and check the nodes you passed through along the way, you'll find that there is often one point along the way where you change direction.
reason.. you got me.. I can only speculate and not too convincingly lol.
I always tell clients, top rankings are great!
SEO can help, top 10 is awesome.. but NEVER NEVER NEVER take your eye off the real goal.. Profit. There are a million other ways to drive targeted traffic and some can have a much higher conversion rate than
SEO. Don't put all your eggs in one basket, balance your marketing so that when you happen to disappear from google for a day your staff doesn't sit around waiting for the "You've got mail" beep on their computer...
maybe this one was 3 cents worth? lol.. =o)