I have noticed over the past week or two that some of the pages from my other websites would disappear from Google’s index and then few days later would appear again. One particular site got hit real hard since from about 200 pages I was left with only 3 for a few days. This of course reflected in the amount of traffic to my site. Fortunately today most of the pages are in the Google’s index again.
Along the way I also have noticed that it only happened to the the websites that had Google’s page rank of 0. Websites that had a page rank of 1 and more were not affected as much, although these sites had pages ranked at 0. This made me think that if you have few high quality “back links” your site will be just fine.
Backlinks, backlinks, backlinks! This seams to be the the answer.