Nothing in optimizing a site for search engines happens quickly. The final result that most are looking for when optimizing a site is higher search engine rankings, and those can take months to develop, and the rest of your websites life to maintain.
Social bookmarking has allowed for a relatively quick fix in the SEO world. It does this by offering someone looking to optimize their pages a way to quickly build links and alert search engines of fresh content.
Bookmarking is the new force in inbound link building. Now instead of just creating link bait in terms of optimized content and waiting for someone to stumble upon it, you can break up your link bait into little packages and take it to your audiences door step. You are able to tell those linking to you what the content is, why it is important, and what keywords are related to it through the use of tags. Compelling content is still a must if you want to capture the exponential traffic and inbound links possible with social bookmarking, but now you do not need to have a large amount of traffic flowing through your site to get the links pointing to you.
Most social networks have a high PageRank with Google, and they are being spidered on almost a constant basis. This allows for your content to be indexed faster, and thus your valuable content can be seen by more people in a timely manner. This is key if you have time sensitive content you are trying to use to draw traffic. It is also important for search engines such as MSN that use a site's "freshness" as a factor in their algorithm.
When all is said and done SEO is just a series of strategies to make sure your website gets the most traffic it possibly can. For this end result social bookmarking offers a quick fix. It can offer an instant stream of traffic, and give you fuel for a future of inbound links that will help increase your PageRank and search engine rankings.