Everybody owes it to themselves to go to Macromedia’s website to find out what sites have stored persistent data on your computer so they can track your activities:
http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html
Lots of weird sites there, I removed them all since I don’t remember visiting most of them and I doubt I’ll miss them anyway, they’ll probably miss me more now that they can’t spy on me anymore 
Clearing out your third party cookies from time to time in Firefox is also a wise move. Unfortunately it’s almost impossible to allow only some third party cookies but disable the rest. For that you will need some kind of specialized add-on. Good luck in finding one, I will start investigating today.
Just a big FYI, Most of these persistent Flash cookies and normal browser cookies can even violate your local legislations. Do you know what they store in your browser, does the website’s privacy policy explain in detail what information is gathered and what purposes it is used for? Do you even know what third party sites you consented to track your movement on the Internet? I bet you don’t, most of us don’t… Some countries demand that companies clearly state this information and make it (easily?) available to everyone. Yea right. People are lazy, and the information is hidden behind minimal footnote links behind dozens of links. Happy hunting!
http://eur-lex.europa.eu/…numdoc=32002L0058&model=guichett
Seriously, people need to be aware. And those who aren’t, need to be locked out and kept safe by default. Like any safe operating system, you are locked down by default and only open incoming data ports when you specifically need it and ask for it. Same should go for third party cookies and shit. No by default, yes only when it’s needed. Rarely should be!
Right now Firefox and all other browsers happily suck in everything from everywhere and keeps it for an unspecified length of time. How did we ever get into this situation that accepting all (most) third party cookies is mandatory. Many big sites refuse to function properly if they’re not enabled.
Link of the day:
https://www.google.com/dashboard/
Go check what data Google has stored, how many email conversations there are on record, if all your search history is being logged, your Orkut contacts etc. etc. There can be lots of information there. And while you’re at it, you can update any information that is wrong or outdated
Also, very much worth a read:
[...] on my 3rd party time blog entry February 1st, 2010 | Category: [...]