In today's mail, this question:
Stupid question that I wish you would address: Are the tissue samples left from recently extinct species such as the Auroch, passenger pigeon, moa, dodo etc etc of sufficient quality to use it to resurrect the species? I would much rather see an Auroch than a pet cat cloned. Of course a wooly mammoth or Neanderthal would be even more interesting but also more problematic.
It seems that those pursuing the idea of such resurrection are more interested in constructing artificial chromosomes. Once the technology is sufficient to do that, all you need is a genome sequence of the extinct organism and a suitable (closely related) host species to carry the pregnancy—of course with the attendant possible problems of immunocompatibility, etc.
So, the barrier now is not the amount of tissue or the availability of genomic data, both of which seem to be sufficient for any recently extinct organism.
I also mentioned the topic last month, after the NY Times carried an article about mammoth cloning. The idea raised there by George Church (which he thought would "alarm a minimal number of people" was constructing a Neandertal genome from a chimpanzee prototype. Is he imagining that people aren't ooked out by a Neandertal baby C-sectioned from a female chimpanzee?
OK, so I'm ooked out. Meanwhile, I think you're going to want to construct a diploid genome, not two identical ones, because there are going to be some recessive lethals in there. So it takes more knowledge of variation than a single genome, and ideally quite a bit more. That's a limit too.