chicagohh - 6:37 pm on Nov 9, 2004 (gmt 0)

Even GG has suggested on more than one occasion that there is nothing you can do that could affect somebody else’s site in the serps. What is your experience with this?

GG is trying to keep things that should be a secret - a secret.

From Googles webmaster facts page (bold added):

There is almost nothing a competitor can do to harm your ranking or have your site removed from our index.

There is some wiggle room in that 'almost nothing' phrase.