Since Barry DiGregorio is no longer allowed to post here, I'll mention he has an online article in Chemical Innovation magazine on Mars Sample Return:

The dilemma of Mars sample return
http://pubs.acs.org/subscribe/journals/ci/31/special/digreg/08digregorio.html

A good list of articles on the issue of planetary protection can be found on Barry's site: www.icamsr.org.

The viewpoint of Dr. Jeffrey Bada, who is developing an organics detector instrument for NASA, on MSR are given in a later article:

Revisiting the Mars sample return debate
http://pubs.acs.org/subscribe/journals/ci/31/i09/html/09postscript.html

Using his instrument, Bada was able to confirm Gil Levin's contention that the Viking organic detector was insensitive to low numbers of microbes:

Vikings would have missed life on Mars
Nature Science Update
Tuesday 13 February 2001
http://www.nature.com/nsu/010215/010215-11.html

Bob Clark