Do you ever notice that sometimes your web site appears in the organic search engine results and then the following day the site is just gone?
This seems to just happen at Google and usually with sites that haven’t been around for that long.
Sometimes it can be a result of a penalty imposed by Google for breaking any of their search engine guidelines. Sometimes its hard to tell because I have sites that were well ranked, then all of a sudden drop out for a week, then come back but not as strong, until later.
As an example, I have a legal directory at www.lawfirm-directory.com and it was always well ranked at Google for a number of terms including "lawfirm directory", then it dropped out for a few weeks, but came back and slowly worked back to the previous listings. NOW its better positioned and we are #3 for lawfirm directory and #10 for law firm directory at Google. #1 at MSN and Yahoo.
I don’t see much ranking fluctuation at MSN or Yahoo and once your site is in at MSN or Yahoo, it usually stays there. Unless of course your talking about the Yahoo directory, which you have to pay $299 annually to be included in.
So be patient if you see your rankings fluctuate, I know it cant be frustrating but if you have a good solid web site, usually things get back to normal pretty quickly.