I had someone submit my a site of mine to numerous bookmarking sites about a month ago (it gave me pretty decent traffic). If I were to have a different person submit the same URL to the same social bookmarking sites would my URL be penalized in any way or have someone else negative happen to me?
Probably not, unless you have alot of people submitting the same link with the exact same description. And the worst that may come from that is your site getting blacklisted by the bookmarking site.