Help Me Understand - Ranking in Google

Don't blast me, as I'm trying to make sense of this and protect my sites in the future. I have a handful of niche sites, each between 3-4 months old. They were ranking well for many of keywords, some on page 1, most on page 2. They mostly reached this spot thru article marketing and forum profiles, plus a purchased WSO article marketing package. I wanted to try and give them a little push to the next level and get my KW's on page 1. I simply submitted two of my sites to a dozen social bookmarking sites. Then the bottom dropped out the very next day, gone from page 1&2 to page 66 and page 101 and so on.

The pages on my site that rank the highest all have my "tag" with the URL, for example:

www.dogtraining.com/tag/obedience-school/

My sites have been like this for about 3 weeks, in the meantime, I continue to build links to my dropped sites in the hope that they will come back.

Has anyone seen this before...both the "tag" post ranking in Google and being dropped so sharply?

Thanks,
Kevin