The biggest danger from social bookmarking is that you'll spend a lot of time doing it that could better be spent on productive marketing tasks.
There are two major issues with social bookmarking:
1. If the only thing you ever submit to the bookmarking site is your own content, you could be labeled a spammer. At the very least, the other people on the site will stop paying attention to your posts, and you may find yourself kicked off of some sites. To be an effective and respected member of the community, you have to submit content from other sites. One rule of thumb I have heard is to aim for only one out of every 10 of your submissions to be for your own content. The other nine should point to someone else's site.
2. If one of your submissions becomes popular, you may see a huge increase in traffic to your site. However, traffic from social bookmarking sites seldom converts -- people jump in to see where the link from the bookmarking site leads, then they leave right away without doing anything on your site.
Submit as much as you want, as often as you want. Just don't expect it to do much of anything to benefit your business.