There seems to be a flurry of new posters that recently launched a new Site with good initial SERPs and then it suddenly disappeared!
These are classic symptoms of what has been dubbed the "Sandbox Effect".
Quoting Garrett French:
"I reported recently on a Google phenomenon in which newly listed sites rank well for two to three weeks and then drop completely out of the top 1000. Often these newly dropped sites have high page rank and don't show for even the least competitive of terms."...
Read more here:
Quoting Jakob Jelling:
"In the age of fair competition you may find it hard to believe that a search engine may hinder the appearance of a new website.
This is what is currently believed to be happening on more web servers today. Some programmers have viewed Google as uncomfortable to rank newer websites until they have proven their viability to exist for more than a period of "x" months. Thus the term "Sandbox Effect" applies to the idea that all new websites have their ratings placed in a holding tank until such time is deemed appropriate before a ranking can commence."
Read more here:
It is important to note that this "Sandbox" phenomenen seems to still being practiced and is thought to be an anti-Spam Website filter.
Ken