Using Bookmarking Sites, may not help you or your site in anyway. My suggestion will be to spend your time in writing quality content for your site's visitors. Concentrate on content instead of links which may not help in anyway.
Why spam via bookmarking services and pollute the web with crap?
Rely on your users to submit you because your site and its content is actually worth it.
Fresh content gives more results whrn compared to social bookmarking but bookmarking is not spamming though. If you bookmark in good sites then it is always helpful.
The original question was about "private bookmarking networks", NOT "social bookmarking".
Any replies that refer to don't answer the original question will be treated as fluff and deleted.
I suggest you to avoid bookmarking submitter and directory submitter software ...... just try to use some hight pr bookmarking sites and concentrate on that you will sure get good result from that ... If you use bookmarking submitter software than its possible that google count that as spam.
How does Google even know that you are even using bookmarking submitter software? Should I use bookmarking submitter software on my competitors sites to get them a spam penalty?