How to efficiently StumbleUpon?

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I have used StumbleUpon to promote my photos in Triond. But after I have clicked "I like it" in StumbleUpon toolbar, my website didn't show in my "favorites" or "pages liked". And I waited for some days, my website still didn't appear. And then I checked the website reviews of StumbleUpon, but it said "we don't have a record", which meant my submittion failed. I don't know why and have tried to submit the website again or only submit the pictures, but all failed! I am so sad and sincerely want to know your experiences in StumbleUpon. And if you have any ideas about how to promote the websites by the social bookmarking such as Digg or StumbleUpon, I deeply hope you could share with me. Thanks for sharing!