SNP research, like the rest of genome research, is definitely a work in progress. No one knows how many SNPs there are, but some people estimate that there could be as many as 10 million. When scientists are sequencing DNA in drug or disease research and they see a discrepancy in the sequence between people, they will record that in a public SNP database. Right now there are about two million entries like that in public databases. There are far fewer well-annotated SNPs; those are SNPs that have been seen at least twice by researchers.