Links are doing bad more then good

[motionz]

First of all, let me be clear with you that. Social Bookmarking and forum posting are not actually link building. Yeah, some time it may happen that when you gain a link to your site it takes a while to determine by the search engines that it is good or not. But since you said that your ranks are gradually falling so its pretty sure that they are hurting your site. Check your link profile through the webmasters tool see whether is any odd links (those are irrelevant to your niche). My guess is that while doing social bookmarking which is basically used to outreach to the larger audience you have gained some bad links.