If you read it on Slashdot, you can skip this post
Some guy writes about a flash web privacy thing with high importance, that I believe many people (incl. me) have never heard about.
Bottom line: the browser options "delete all cookies" or "clear all private data" are not doing 100% of the job. Flash local data can be deleted from here (on Macromedia.com)[1].
Also, you're using flashblock, right?
[1] I wonder how they secure that thing: after all it's a flash app with privileges for messing with the client's settings!