As you most likely know, social bookmarking as a marketing and backlinking strategy has been around for a few years. There appears to be no let-up with their popularity, especially for off-page SEO purposes. But you really should never neglect or overlook what could be done for the more long-term methods at high PR bookmarking sites. So it all just is dependent upon what you want to do in your business. Yes, bookmarks can be kept in your account at bookmarking sites, although they have become community centers for lots of people. You can designate tags (keywords) to your bookmarks, and that actually has SEO benefits but a lot depends on the particular site.
We need not look for further examples than SEO Link Monster. A couple of years ago the more popular bookmark sites changed all their links to nofollow which had a huge effect on bookmark rankings. Sites like Technorati and Digg, plus a few others, were able to dominate the first pages of SERPS in Google as a result of their high PR status. But I would not be surprised if that took place.
Even so there is a great deal you can do with certain approaches at these highly trafficked sites. What can result in issues with so many profiles for backlinking is those profiles are not properly written or anything similar to high quality. Profiles that have appearances of being legitimate will do a greater job for you and have a great chance of passing a review. Hopefully you realize the great benefit offered when you take an approach encompassing a higher quality profile.
Also consider your ability to use the RSS feed functions available with a meaty profile with good content in it. You can promote your RSS feed at other places and RSS directories. You may include your various links plus precise content in your feeds, too.
Just look at your feeds, and you can know when you’re going too far with promotional links, etc. You can accomplish a lot if you have solid relationships in place at bookmarking sites. The better quality profile strategy is something you ought to check out, and you may like the results.