I've never heard of this happening before. I mean, what's the point of social bookmarking if you can't bookmark more than one page at a time?
However, it may be up to the bookmark administrators of each social bookmarking site. If they think you're being too spammy, they may delete your bookmarks or ban your account altogether. There is no Google penalty.
The great thing about bookmarks is that you get permanent backlinks from them, not like Press Release backlinks that only last 6 months until the next series of news comes in.
From Google's perspective, when you're doing backlinking, you want to make your backlinks look as natural as possible. That means the links should be diverse, relevant, come from authority sites (preferably PR3 and up) and spread out.
The truth is you cannot control who on the internet will link to you or not link to you. So when Google sees this, it thinks, "Okay. Everything looks hunky dory to me." That's why you want backlinking to seem as natural as possible.
You want your site to appear like an authority site, so when your pages are getting that awesome linkjuice from a PR 7 site, etc. It helps boost your pages up the ranks of Google search engines.
The best way for to have book marks be effective for backlinking is to get other people to bookmark your sites for you. That shows Google that different people from different IP addresses (not just your own) really like your stuff, so your Hubs or pages are considered authority content.
Page ranking by Google has over 200 criteria. There's no way to keep track of all the criteria, but backlinks and low competition keywords which you optimize your pages for make all the difference.
If you want to know of a great site that has a community of people who will bookmark your links for you while you bookmark their in return, I recommend reading this Squidoo Lens: http://www.squidoo.com/social-adr-an-ingenius-way-...