It has been observed that links appearing on first page, after a month, are gone to somewhere else?? Does google changes its algorithm of dancing??
I would assume your website is still a new one, not reach one year old yet. This is a pretty common for new website being ranked quite good in a first phase before dropped. A so called myth "Sandbox" but I would calling them a filter probation period instead. Just look around the forums and you would see a tons of thread discussed about the issues already.
A new site doesn't have to compete against the ebays and amazons of the world. I could be number 1 result in the PR1 group, but 100000 in the total search results. I believe that a good search engine should support multiple ways to present results (and even rank results differently) based on what we think people might want. It's true that Google leans more toward search than serendipity, but it would be nice if Google gave users ways to tilt things a little more.
Google would not be changing the algo so frequently but serps being dynamic in nature... they surely get influenced by other people's efforts with respect to yours, to bring about such a change! Regards, RightMan