Here is a link to the interview with the ESA scientist. I am a little disturbed that he declares that it is his intention to demonstrate that life exists on Mars by end of the summer. Doesn't exactly seem open-minded.

http://www.earthfiles.com/news/news.cfm?ID=707&category=Science

Nonetheless, there was this tidbit:

"If the methane on Mars were due to OH photochemistry in the Martian atmosphere, then methane should have a life time of 300-400 years and should be uniform throughout the entire atmosphere. But it is not uniform. So there must be a 'sink' of methane somewhere. On Earth there are sinks of methane with OH and oxidation with oxygen in the Earth's atmosphere which are indications of biological activity and can be linked to biological things in the soil."

If I read that correctly, it means he has found the methane distribution is non-uniform. That is interesting, since it seems like it would argue against an upper atmospheric process, and for a ground-based source. I'd be far more likely to believe that source is related to volcanism, maybe slow outgassing from magma bodies somewhere, but even so that would be a very significant finding.