Clear cookies/reset browser doesn't delete your Flash cookies
bits.blogs.nytimes.com
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Paul from Meebo gave a great presentation on all the sneaky persistence options a few months ago: http://www.slideshare.net/idontsmoke/client-side-storage
Interesting takeaway: more visitors have some form of persistent storage than have cookies enabled.
I found the stats at the end to be deceptive though. You'd have to code support for 3 different native client storage APIs in JavaScript + use Flash in order to cover enough users to rival cookies. It's no wonder most web devs just use cookies.
I haven't had a chance (or need) to use it yet.
There are still a large number of people who have terrible problems managing web site logins. Reducing the barriers to using your site for returning visitors is definitely a goal with a lot of value and clear ROI.
Here's a way to manage plugin settings on Mac:
http://www.macromedia.com/support/documentation/en/flashplay...