My company has a little widget that plugs into shopping carts. We are running into a problem where setting cookies in IE7 is not working. This is happening because we are
The Fiddler web debugger (www.fiddler2.com) has a "Privacy" inspector tab on the response which decodes the P3P tokens into their meanings. There's a link at the bottom of the inspector which points to the MSDN article that shows which policies are considered "acceptable" by default.
Note, of course, that P3P policies are a Legal declaration, so you must be sure that your use of cookies matches what you claim in P3P.