yes that is one of the helpful in improving the PR of any site is a social bookmarking and especially this one as the beautiful things you can do in a campaign can help it to a campaign.
To increase page rank of your site try to get as many quality backlinks from high pr sites those page rank lie between 3-7 through which your site page rank will also improves.
To maintain and increase page rank, you have to get more quality links...... try to get links on niche domain......
I suggested only improve or build relevant back-link, PR not necessary Relevancy is matter. And Second improved your site service or content. Thanks
you have to promote you websites in high pr rank sites and try to get more back links from high pr sites.
i recently heard that SEOMoz Domain authority is now more important than PR. Has anyone else here this before?