In mid-2006 when I finally managed to snag a Google Analytics account I was working with an internet acquaintance on some upgrades to their site. One of these upgrades included stat tracking with GA. The acquaintance and I both had an account, so we thought: "Hey, why not, invite me to your stats!"
Now, four-ish years later, I am no longer in contact with that acquaintance and am not affiliated with the project at all, and yet - I can still see their GA stats. All due to a simple flaw in the GA system: You can't remove shared GA accounts from one another.
I now have two "Accounts" listed when I first visit the Dashboard. One "private" the other of the acquaintance. I can still see their stats for all their accounts (apparently the entire account was shared with me, not only a single site).
There's an ongoing discussion the Google Support forums, but no reaction from Google whatsoever.
Check out the discussion here.